| Message ID | 20250330-wip-obbardc-qcom-t14s-oled-panel-brightness-v3-1-156801d97a8a@linaro.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v3] drm/dp: clamp PWM bit count to advertised MIN and MAX capabilities | expand |
On Sun, Mar 30, 2025 at 05:31:20PM +0100, Christopher Obbard wrote: > According to the eDP specification (VESA Embedded DisplayPort Standard > v1.4b, Section 3.3.10.2), if the value of DP_EDP_PWMGEN_BIT_COUNT is > less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, the sink is required to use > the MIN value as the effective PWM bit count. > > This commit updates the logic to clamp the reported > DP_EDP_PWMGEN_BIT_COUNT to the range defined by > DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN and _CAP_MAX. This ensures correct > handling of eDP panels that report a zero PWM bit count but still > provide valid non-zero MIN and MAX capability values. Without this > clamping, brightness values may be interpreted incorrectly, leading > to a dim or non-functional backlight. > > For example, the Samsung ATNA40YK20 OLED panel used in the Lenovo > ThinkPad T14s Gen6 (Snapdragon) reports a PWM bit count of 0, but > supports AUX backlight control and declares a valid 11-bit range. > Clamping ensures brightness scaling works as intended on such panels. > > Co-developed-by: Rui Miguel Silva <rui.silva@linaro.org> > Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org> > Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org> > --- > Changes in v3: > - Properly rebase patch on top of latest version of drm-misc-next. > - Make patch more generic by clamping PWM bit count to advertised MIN > and MAX capabilities (suggested by Dmitry). > - Link to v2: https://lore.kernel.org/r/20250327-wip-obbardc-qcom-t14s-oled-panel-brightness-v2-1-16dc3ee00276@linaro.org > > Changes in v2: > - Split backlight brightness patch from T14s OLED enablement series. > - Use PWMGEN_CAP_MIN rather than MAX (Dmitry). > - Rework commit message to reference eDP spec. > - Rebase on drm-misc-next. > - Link to v1: https://lore.kernel.org/all/20250325-wip-obbardc-qcom-t14s-oled-panel-v2-4-e9bc7c9d30cc@linaro.org/ > --- > drivers/gpu/drm/display/drm_dp_helper.c | 48 ++++++++++++++++++++------------- > 1 file changed, 30 insertions(+), 18 deletions(-) > > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c > index e2439c8a7fefe116b04aaa689b557e2387b05540..fcc26cb96a51066a503433b2dc660126155d179c 100644 > --- a/drivers/gpu/drm/display/drm_dp_helper.c > +++ b/drivers/gpu/drm/display/drm_dp_helper.c > @@ -28,6 +28,7 @@ > #include <linux/init.h> > #include <linux/iopoll.h> > #include <linux/kernel.h> > +#include <linux/minmax.h> > #include <linux/module.h> > #include <linux/sched.h> > #include <linux/seq_file.h> > @@ -4033,8 +4034,33 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > aux->name, ret); > return -ENODEV; > } > - Nitpick: please keep the empty line. > pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > + > + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); > + if (ret != 1) { No. Please take a look a few lines below, where you are removing corresponding lines. > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", > + aux->name, ret); > + return -ENODEV; Hmm. Why? It was 'return 0' before and your commit message contains no explanation. > + } > + pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > + > + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); > + if (ret != 1) { > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", > + aux->name, ret); > + return -ENODEV; > + } > + pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > + > + /* > + * Per VESA eDP Spec v1.4b, section 3.3.10.2: > + * If DP_EDP_PWMGEN_BIT_COUNT is less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, > + * the sink must use the MIN value as the effective PWM bit count. > + * Clamp the reported value to the [MIN, MAX] capability range to ensure > + * correct brightness scaling on compliant eDP panels. > + */ > + pn = clamp(pn, pn_min, pn_max); > + > bl->max = (1 << pn) - 1; > if (!driver_pwm_freq_hz) > return 0; > @@ -4054,29 +4080,15 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > */ > fxp = DIV_ROUND_CLOSEST(1000 * DP_EDP_BACKLIGHT_FREQ_BASE_KHZ, driver_pwm_freq_hz); > > - /* Use highest possible value of Pn for more granularity of brightness adjustment while > + /* > + * Ensure frequency is within 25% of desired value. > + * Use highest possible value of Pn for more granularity of brightness adjustment while Huh? I don't see a corresponding code change. If you are fixing the comment, it should come as a separate commit. > * satisfying the conditions below. > * - Pn is in the range of Pn_min and Pn_max > * - F is in the range of 1 and 255 > * - FxP is within 25% of desired value. > * Note: 25% is arbitrary value and may need some tweak. > */ > - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); > - if (ret < 0) { > - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", > - aux->name, ret); > - return 0; > - } > - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); > - if (ret < 0) { > - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", > - aux->name, ret); > - return 0; > - } > - pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > - pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > - > - /* Ensure frequency is within 25% of desired value */ > fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4); > fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4); > if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
Hi Dmitry, On Sun, 30 Mar 2025 at 17:42, Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com> wrote: > > On Sun, Mar 30, 2025 at 05:31:20PM +0100, Christopher Obbard wrote: > > According to the eDP specification (VESA Embedded DisplayPort Standard > > v1.4b, Section 3.3.10.2), if the value of DP_EDP_PWMGEN_BIT_COUNT is > > less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, the sink is required to use > > the MIN value as the effective PWM bit count. > > > > This commit updates the logic to clamp the reported > > DP_EDP_PWMGEN_BIT_COUNT to the range defined by > > DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN and _CAP_MAX. This ensures correct > > handling of eDP panels that report a zero PWM bit count but still > > provide valid non-zero MIN and MAX capability values. Without this > > clamping, brightness values may be interpreted incorrectly, leading > > to a dim or non-functional backlight. > > > > For example, the Samsung ATNA40YK20 OLED panel used in the Lenovo > > ThinkPad T14s Gen6 (Snapdragon) reports a PWM bit count of 0, but > > supports AUX backlight control and declares a valid 11-bit range. > > Clamping ensures brightness scaling works as intended on such panels. > > > > Co-developed-by: Rui Miguel Silva <rui.silva@linaro.org> > > Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org> > > Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org> > > --- > > Changes in v3: > > - Properly rebase patch on top of latest version of drm-misc-next. > > - Make patch more generic by clamping PWM bit count to advertised MIN > > and MAX capabilities (suggested by Dmitry). > > - Link to v2: https://lore.kernel.org/r/20250327-wip-obbardc-qcom-t14s-oled-panel-brightness-v2-1-16dc3ee00276@linaro.org > > > > Changes in v2: > > - Split backlight brightness patch from T14s OLED enablement series. > > - Use PWMGEN_CAP_MIN rather than MAX (Dmitry). > > - Rework commit message to reference eDP spec. > > - Rebase on drm-misc-next. > > - Link to v1: https://lore.kernel.org/all/20250325-wip-obbardc-qcom-t14s-oled-panel-v2-4-e9bc7c9d30cc@linaro.org/ > > --- > > drivers/gpu/drm/display/drm_dp_helper.c | 48 ++++++++++++++++++++------------- > > 1 file changed, 30 insertions(+), 18 deletions(-) > > > > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c > > index e2439c8a7fefe116b04aaa689b557e2387b05540..fcc26cb96a51066a503433b2dc660126155d179c 100644 > > --- a/drivers/gpu/drm/display/drm_dp_helper.c > > +++ b/drivers/gpu/drm/display/drm_dp_helper.c > > @@ -28,6 +28,7 @@ > > #include <linux/init.h> > > #include <linux/iopoll.h> > > #include <linux/kernel.h> > > +#include <linux/minmax.h> > > #include <linux/module.h> > > #include <linux/sched.h> > > #include <linux/seq_file.h> > > @@ -4033,8 +4034,33 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > > aux->name, ret); > > return -ENODEV; > > } > > - > > Nitpick: please keep the empty line. Sure. > > pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > + > > + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); > > + if (ret != 1) { > > No. Please take a look a few lines below, where you are removing > corresponding lines. Hmm, the original code which reads CAP_MIN and CAP_MAX both check if ret != 1 too, am I missing something ? > > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", > > + aux->name, ret); > > + return -ENODEV; > > Hmm. Why? It was 'return 0' before and your commit message contains no > explanation. Yeah, basically returning 0 here would not set bl->max but indicate success. Is my logic correct? I will simply update the commit message if so. > > + } > > + pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > + > > + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); > > + if (ret != 1) { > > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", > > + aux->name, ret); > > + return -ENODEV; > > + } > > + pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > + > > + /* > > + * Per VESA eDP Spec v1.4b, section 3.3.10.2: > > + * If DP_EDP_PWMGEN_BIT_COUNT is less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, > > + * the sink must use the MIN value as the effective PWM bit count. > > + * Clamp the reported value to the [MIN, MAX] capability range to ensure > > + * correct brightness scaling on compliant eDP panels. > > + */ > > + pn = clamp(pn, pn_min, pn_max); > > + > > bl->max = (1 << pn) - 1; > > if (!driver_pwm_freq_hz) > > return 0; > > @@ -4054,29 +4080,15 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > > */ > > fxp = DIV_ROUND_CLOSEST(1000 * DP_EDP_BACKLIGHT_FREQ_BASE_KHZ, driver_pwm_freq_hz); > > > > - /* Use highest possible value of Pn for more granularity of brightness adjustment while > > + /* > > + * Ensure frequency is within 25% of desired value. > > + * Use highest possible value of Pn for more granularity of brightness adjustment while > > Huh? I don't see a corresponding code change. If you are fixing the > comment, it should come as a separate commit. Sure. I will drop this hunk. I folded it into this commit as it was a leftover artifact of moving the code around. > > > * satisfying the conditions below. > > * - Pn is in the range of Pn_min and Pn_max > > * - F is in the range of 1 and 255 > > * - FxP is within 25% of desired value. > > * Note: 25% is arbitrary value and may need some tweak. > > */ > > - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); > > - if (ret < 0) { > > - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", > > - aux->name, ret); > > - return 0; > > - } > > - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); > > - if (ret < 0) { > > - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", > > - aux->name, ret); > > - return 0; > > - } > > - pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > - pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > - > > - /* Ensure frequency is within 25% of desired value */ > > fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4); > > fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4); > > if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) { > > -- > With best wishes > Dmitry
On Sun, 30 Mar 2025 at 20:11, Christopher Obbard <christopher.obbard@linaro.org> wrote: > > Hi Dmitry, > > On Sun, 30 Mar 2025 at 17:42, Dmitry Baryshkov > <dmitry.baryshkov@oss.qualcomm.com> wrote: > > > > On Sun, Mar 30, 2025 at 05:31:20PM +0100, Christopher Obbard wrote: > > > According to the eDP specification (VESA Embedded DisplayPort Standard > > > v1.4b, Section 3.3.10.2), if the value of DP_EDP_PWMGEN_BIT_COUNT is > > > less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, the sink is required to use > > > the MIN value as the effective PWM bit count. > > > > > > This commit updates the logic to clamp the reported > > > DP_EDP_PWMGEN_BIT_COUNT to the range defined by > > > DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN and _CAP_MAX. This ensures correct > > > handling of eDP panels that report a zero PWM bit count but still > > > provide valid non-zero MIN and MAX capability values. Without this > > > clamping, brightness values may be interpreted incorrectly, leading > > > to a dim or non-functional backlight. > > > > > > For example, the Samsung ATNA40YK20 OLED panel used in the Lenovo > > > ThinkPad T14s Gen6 (Snapdragon) reports a PWM bit count of 0, but > > > supports AUX backlight control and declares a valid 11-bit range. > > > Clamping ensures brightness scaling works as intended on such panels. > > > > > > Co-developed-by: Rui Miguel Silva <rui.silva@linaro.org> > > > Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org> > > > Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org> > > > --- > > > Changes in v3: > > > - Properly rebase patch on top of latest version of drm-misc-next. > > > - Make patch more generic by clamping PWM bit count to advertised MIN > > > and MAX capabilities (suggested by Dmitry). > > > - Link to v2: https://lore.kernel.org/r/20250327-wip-obbardc-qcom-t14s-oled-panel-brightness-v2-1-16dc3ee00276@linaro.org > > > > > > Changes in v2: > > > - Split backlight brightness patch from T14s OLED enablement series. > > > - Use PWMGEN_CAP_MIN rather than MAX (Dmitry). > > > - Rework commit message to reference eDP spec. > > > - Rebase on drm-misc-next. > > > - Link to v1: https://lore.kernel.org/all/20250325-wip-obbardc-qcom-t14s-oled-panel-v2-4-e9bc7c9d30cc@linaro.org/ > > > --- > > > drivers/gpu/drm/display/drm_dp_helper.c | 48 ++++++++++++++++++++------------- > > > 1 file changed, 30 insertions(+), 18 deletions(-) > > > > > > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c > > > index e2439c8a7fefe116b04aaa689b557e2387b05540..fcc26cb96a51066a503433b2dc660126155d179c 100644 > > > --- a/drivers/gpu/drm/display/drm_dp_helper.c > > > +++ b/drivers/gpu/drm/display/drm_dp_helper.c > > > @@ -28,6 +28,7 @@ > > > #include <linux/init.h> > > > #include <linux/iopoll.h> > > > #include <linux/kernel.h> > > > +#include <linux/minmax.h> > > > #include <linux/module.h> > > > #include <linux/sched.h> > > > #include <linux/seq_file.h> > > > @@ -4033,8 +4034,33 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > > > aux->name, ret); > > > return -ENODEV; > > > } > > > - > > > > Nitpick: please keep the empty line. > > Sure. > > > > > pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > + > > > + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); > > > + if (ret != 1) { > > > > No. Please take a look a few lines below, where you are removing > > corresponding lines. > > Hmm, the original code which reads CAP_MIN and CAP_MAX both check if > ret != 1 too, am I missing something ? Yes, you do. Please scroll this email a few lines down. > > > > > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", > > > + aux->name, ret); > > > + return -ENODEV; > > > > Hmm. Why? It was 'return 0' before and your commit message contains no > > explanation. > > Yeah, basically returning 0 here would not set bl->max but indicate > success. Is my logic correct? I will simply update the commit message > if so. Please describe that in the commit message why it's required for those two reg reads to succeed. > > > > > + } > > > + pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > + > > > + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); > > > + if (ret != 1) { > > > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", > > > + aux->name, ret); > > > + return -ENODEV; > > > + } > > > + pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > + > > > + /* > > > + * Per VESA eDP Spec v1.4b, section 3.3.10.2: > > > + * If DP_EDP_PWMGEN_BIT_COUNT is less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, > > > + * the sink must use the MIN value as the effective PWM bit count. > > > + * Clamp the reported value to the [MIN, MAX] capability range to ensure > > > + * correct brightness scaling on compliant eDP panels. > > > + */ > > > + pn = clamp(pn, pn_min, pn_max); > > > + > > > bl->max = (1 << pn) - 1; > > > if (!driver_pwm_freq_hz) > > > return 0; > > > @@ -4054,29 +4080,15 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > > > */ > > > fxp = DIV_ROUND_CLOSEST(1000 * DP_EDP_BACKLIGHT_FREQ_BASE_KHZ, driver_pwm_freq_hz); > > > > > > - /* Use highest possible value of Pn for more granularity of brightness adjustment while > > > + /* > > > + * Ensure frequency is within 25% of desired value. > > > + * Use highest possible value of Pn for more granularity of brightness adjustment while > > > > Huh? I don't see a corresponding code change. If you are fixing the > > comment, it should come as a separate commit. > > Sure. I will drop this hunk. > I folded it into this commit as it was a leftover artifact of moving > the code around. Please refrain from folding unrelated changes. > > > > > > * satisfying the conditions below. > > > * - Pn is in the range of Pn_min and Pn_max > > > * - F is in the range of 1 and 255 > > > * - FxP is within 25% of desired value. > > > * Note: 25% is arbitrary value and may need some tweak. > > > */ > > > - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); > > > - if (ret < 0) { > > > - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", > > > - aux->name, ret); > > > - return 0; > > > - } > > > - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); > > > - if (ret < 0) { > > > - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", > > > - aux->name, ret); > > > - return 0; > > > - } > > > - pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > - pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > - > > > - /* Ensure frequency is within 25% of desired value */ > > > fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4); > > > fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4); > > > if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) { > > > > -- > > With best wishes > > Dmitry
Hi Dmitry, On Sun, 30 Mar 2025 at 18:17, Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com> wrote: > > On Sun, 30 Mar 2025 at 20:11, Christopher Obbard > <christopher.obbard@linaro.org> wrote: > > > > Hi Dmitry, > > > > On Sun, 30 Mar 2025 at 17:42, Dmitry Baryshkov > > <dmitry.baryshkov@oss.qualcomm.com> wrote: > > > > > > On Sun, Mar 30, 2025 at 05:31:20PM +0100, Christopher Obbard wrote: > > > > According to the eDP specification (VESA Embedded DisplayPort Standard > > > > v1.4b, Section 3.3.10.2), if the value of DP_EDP_PWMGEN_BIT_COUNT is > > > > less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, the sink is required to use > > > > the MIN value as the effective PWM bit count. > > > > > > > > This commit updates the logic to clamp the reported > > > > DP_EDP_PWMGEN_BIT_COUNT to the range defined by > > > > DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN and _CAP_MAX. This ensures correct > > > > handling of eDP panels that report a zero PWM bit count but still > > > > provide valid non-zero MIN and MAX capability values. Without this > > > > clamping, brightness values may be interpreted incorrectly, leading > > > > to a dim or non-functional backlight. > > > > > > > > For example, the Samsung ATNA40YK20 OLED panel used in the Lenovo > > > > ThinkPad T14s Gen6 (Snapdragon) reports a PWM bit count of 0, but > > > > supports AUX backlight control and declares a valid 11-bit range. > > > > Clamping ensures brightness scaling works as intended on such panels. > > > > > > > > Co-developed-by: Rui Miguel Silva <rui.silva@linaro.org> > > > > Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org> > > > > Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org> > > > > --- > > > > Changes in v3: > > > > - Properly rebase patch on top of latest version of drm-misc-next. > > > > - Make patch more generic by clamping PWM bit count to advertised MIN > > > > and MAX capabilities (suggested by Dmitry). > > > > - Link to v2: https://lore.kernel.org/r/20250327-wip-obbardc-qcom-t14s-oled-panel-brightness-v2-1-16dc3ee00276@linaro.org > > > > > > > > Changes in v2: > > > > - Split backlight brightness patch from T14s OLED enablement series. > > > > - Use PWMGEN_CAP_MIN rather than MAX (Dmitry). > > > > - Rework commit message to reference eDP spec. > > > > - Rebase on drm-misc-next. > > > > - Link to v1: https://lore.kernel.org/all/20250325-wip-obbardc-qcom-t14s-oled-panel-v2-4-e9bc7c9d30cc@linaro.org/ > > > > --- > > > > drivers/gpu/drm/display/drm_dp_helper.c | 48 ++++++++++++++++++++------------- > > > > 1 file changed, 30 insertions(+), 18 deletions(-) > > > > > > > > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c > > > > index e2439c8a7fefe116b04aaa689b557e2387b05540..fcc26cb96a51066a503433b2dc660126155d179c 100644 > > > > --- a/drivers/gpu/drm/display/drm_dp_helper.c > > > > +++ b/drivers/gpu/drm/display/drm_dp_helper.c > > > > @@ -28,6 +28,7 @@ > > > > #include <linux/init.h> > > > > #include <linux/iopoll.h> > > > > #include <linux/kernel.h> > > > > +#include <linux/minmax.h> > > > > #include <linux/module.h> > > > > #include <linux/sched.h> > > > > #include <linux/seq_file.h> > > > > @@ -4033,8 +4034,33 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > > > > aux->name, ret); > > > > return -ENODEV; > > > > } > > > > - > > > > > > Nitpick: please keep the empty line. > > > > Sure. > > > > > > > > pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > > + > > > > + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); > > > > + if (ret != 1) { > > > > > > No. Please take a look a few lines below, where you are removing > > > corresponding lines. > > > > Hmm, the original code which reads CAP_MIN and CAP_MAX both check if > > ret != 1 too, am I missing something ? > > Yes, you do. Please scroll this email a few lines down. OK, so just so I understand fully before preparing next version, no change is needed in the logic in this line? Just a commit message change? > > > > > > > > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", > > > > + aux->name, ret); > > > > + return -ENODEV; > > > > > > Hmm. Why? It was 'return 0' before and your commit message contains no > > > explanation. > > > > Yeah, basically returning 0 here would not set bl->max but indicate > > success. Is my logic correct? I will simply update the commit message > > if so. > > Please describe that in the commit message why it's required for those > two reg reads to succeed. Sure. > > > > > > > > > + } > > > > + pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > > + > > > > + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); > > > > + if (ret != 1) { > > > > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", > > > > + aux->name, ret); > > > > + return -ENODEV; > > > > + } > > > > + pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > > + > > > > + /* > > > > + * Per VESA eDP Spec v1.4b, section 3.3.10.2: > > > > + * If DP_EDP_PWMGEN_BIT_COUNT is less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, > > > > + * the sink must use the MIN value as the effective PWM bit count. > > > > + * Clamp the reported value to the [MIN, MAX] capability range to ensure > > > > + * correct brightness scaling on compliant eDP panels. > > > > + */ > > > > + pn = clamp(pn, pn_min, pn_max); > > > > + > > > > bl->max = (1 << pn) - 1; > > > > if (!driver_pwm_freq_hz) > > > > return 0; > > > > @@ -4054,29 +4080,15 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > > > > */ > > > > fxp = DIV_ROUND_CLOSEST(1000 * DP_EDP_BACKLIGHT_FREQ_BASE_KHZ, driver_pwm_freq_hz); > > > > > > > > - /* Use highest possible value of Pn for more granularity of brightness adjustment while > > > > + /* > > > > + * Ensure frequency is within 25% of desired value. > > > > + * Use highest possible value of Pn for more granularity of brightness adjustment while > > > > > > Huh? I don't see a corresponding code change. If you are fixing the > > > comment, it should come as a separate commit. > > > > Sure. I will drop this hunk. > > I folded it into this commit as it was a leftover artifact of moving > > the code around. > > Please refrain from folding unrelated changes. Sure. I will be more careful in future. > > > > > > > > > * satisfying the conditions below. > > > > * - Pn is in the range of Pn_min and Pn_max > > > > * - F is in the range of 1 and 255 > > > > * - FxP is within 25% of desired value. > > > > * Note: 25% is arbitrary value and may need some tweak. > > > > */ > > > > - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); > > > > - if (ret < 0) { > > > > - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", > > > > - aux->name, ret); > > > > - return 0; > > > > - } > > > > - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); > > > > - if (ret < 0) { > > > > - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", > > > > - aux->name, ret); > > > > - return 0; > > > > - } > > > > - pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > > - pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > > - > > > > - /* Ensure frequency is within 25% of desired value */ > > > > fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4); > > > > fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4); > > > > if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) { > > > > > > -- > > > With best wishes > > > Dmitry > > > > -- > With best wishes > Dmitry
On Sun, 30 Mar 2025 at 20:21, Christopher Obbard <christopher.obbard@linaro.org> wrote: > > Hi Dmitry, > > On Sun, 30 Mar 2025 at 18:17, Dmitry Baryshkov > <dmitry.baryshkov@oss.qualcomm.com> wrote: > > > > On Sun, 30 Mar 2025 at 20:11, Christopher Obbard > > <christopher.obbard@linaro.org> wrote: > > > > > > Hi Dmitry, > > > > > > On Sun, 30 Mar 2025 at 17:42, Dmitry Baryshkov > > > <dmitry.baryshkov@oss.qualcomm.com> wrote: > > > > > > > > On Sun, Mar 30, 2025 at 05:31:20PM +0100, Christopher Obbard wrote: > > > > > According to the eDP specification (VESA Embedded DisplayPort Standard > > > > > v1.4b, Section 3.3.10.2), if the value of DP_EDP_PWMGEN_BIT_COUNT is > > > > > less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, the sink is required to use > > > > > the MIN value as the effective PWM bit count. > > > > > > > > > > This commit updates the logic to clamp the reported > > > > > DP_EDP_PWMGEN_BIT_COUNT to the range defined by > > > > > DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN and _CAP_MAX. This ensures correct > > > > > handling of eDP panels that report a zero PWM bit count but still > > > > > provide valid non-zero MIN and MAX capability values. Without this > > > > > clamping, brightness values may be interpreted incorrectly, leading > > > > > to a dim or non-functional backlight. > > > > > > > > > > For example, the Samsung ATNA40YK20 OLED panel used in the Lenovo > > > > > ThinkPad T14s Gen6 (Snapdragon) reports a PWM bit count of 0, but > > > > > supports AUX backlight control and declares a valid 11-bit range. > > > > > Clamping ensures brightness scaling works as intended on such panels. > > > > > > > > > > Co-developed-by: Rui Miguel Silva <rui.silva@linaro.org> > > > > > Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org> > > > > > Signed-off-by: Christopher Obbard <christopher.obbard@linaro.org> > > > > > --- > > > > > Changes in v3: > > > > > - Properly rebase patch on top of latest version of drm-misc-next. > > > > > - Make patch more generic by clamping PWM bit count to advertised MIN > > > > > and MAX capabilities (suggested by Dmitry). > > > > > - Link to v2: https://lore.kernel.org/r/20250327-wip-obbardc-qcom-t14s-oled-panel-brightness-v2-1-16dc3ee00276@linaro.org > > > > > > > > > > Changes in v2: > > > > > - Split backlight brightness patch from T14s OLED enablement series. > > > > > - Use PWMGEN_CAP_MIN rather than MAX (Dmitry). > > > > > - Rework commit message to reference eDP spec. > > > > > - Rebase on drm-misc-next. > > > > > - Link to v1: https://lore.kernel.org/all/20250325-wip-obbardc-qcom-t14s-oled-panel-v2-4-e9bc7c9d30cc@linaro.org/ > > > > > --- > > > > > drivers/gpu/drm/display/drm_dp_helper.c | 48 ++++++++++++++++++++------------- > > > > > 1 file changed, 30 insertions(+), 18 deletions(-) > > > > > > > > > > diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c > > > > > index e2439c8a7fefe116b04aaa689b557e2387b05540..fcc26cb96a51066a503433b2dc660126155d179c 100644 > > > > > --- a/drivers/gpu/drm/display/drm_dp_helper.c > > > > > +++ b/drivers/gpu/drm/display/drm_dp_helper.c > > > > > @@ -28,6 +28,7 @@ > > > > > #include <linux/init.h> > > > > > #include <linux/iopoll.h> > > > > > #include <linux/kernel.h> > > > > > +#include <linux/minmax.h> > > > > > #include <linux/module.h> > > > > > #include <linux/sched.h> > > > > > #include <linux/seq_file.h> > > > > > @@ -4033,8 +4034,33 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > > > > > aux->name, ret); > > > > > return -ENODEV; > > > > > } > > > > > - > > > > > > > > Nitpick: please keep the empty line. > > > > > > Sure. > > > > > > > > > > > pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > > > + > > > > > + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); > > > > > + if (ret != 1) { > > > > > > > > No. Please take a look a few lines below, where you are removing > > > > corresponding lines. > > > > > > Hmm, the original code which reads CAP_MIN and CAP_MAX both check if > > > ret != 1 too, am I missing something ? > > > > Yes, you do. Please scroll this email a few lines down. > > OK, so just so I understand fully before preparing next version, no > change is needed in the logic in this line? Just a commit message > change? Let me do that for you. This is from your patch: @@ -4061,21 +4088,6 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf * - FxP is within 25% of desired value. * Note: 25% is arbitrary value and may need some tweak. */ - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); - if (ret < 0) { ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ So... I don't know what to say here. > > > > > > > > > > > > > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", > > > > > + aux->name, ret); > > > > > + return -ENODEV; > > > > > > > > Hmm. Why? It was 'return 0' before and your commit message contains no > > > > explanation. > > > > > > Yeah, basically returning 0 here would not set bl->max but indicate > > > success. Is my logic correct? I will simply update the commit message > > > if so. > > > > Please describe that in the commit message why it's required for those > > two reg reads to succeed. > > Sure. > > > > > > > > > > > > > > + } > > > > > + pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > > > + > > > > > + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); > > > > > + if (ret != 1) { > > > > > + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", > > > > > + aux->name, ret); > > > > > + return -ENODEV; > > > > > + } > > > > > + pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > > > + > > > > > + /* > > > > > + * Per VESA eDP Spec v1.4b, section 3.3.10.2: > > > > > + * If DP_EDP_PWMGEN_BIT_COUNT is less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, > > > > > + * the sink must use the MIN value as the effective PWM bit count. > > > > > + * Clamp the reported value to the [MIN, MAX] capability range to ensure > > > > > + * correct brightness scaling on compliant eDP panels. > > > > > + */ > > > > > + pn = clamp(pn, pn_min, pn_max); > > > > > + > > > > > bl->max = (1 << pn) - 1; > > > > > if (!driver_pwm_freq_hz) > > > > > return 0; > > > > > @@ -4054,29 +4080,15 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf > > > > > */ > > > > > fxp = DIV_ROUND_CLOSEST(1000 * DP_EDP_BACKLIGHT_FREQ_BASE_KHZ, driver_pwm_freq_hz); > > > > > > > > > > - /* Use highest possible value of Pn for more granularity of brightness adjustment while > > > > > + /* > > > > > + * Ensure frequency is within 25% of desired value. > > > > > + * Use highest possible value of Pn for more granularity of brightness adjustment while > > > > > > > > Huh? I don't see a corresponding code change. If you are fixing the > > > > comment, it should come as a separate commit. > > > > > > Sure. I will drop this hunk. > > > I folded it into this commit as it was a leftover artifact of moving > > > the code around. > > > > Please refrain from folding unrelated changes. > > Sure. I will be more careful in future. > > > > > > > > > > > > > > * satisfying the conditions below. > > > > > * - Pn is in the range of Pn_min and Pn_max > > > > > * - F is in the range of 1 and 255 > > > > > * - FxP is within 25% of desired value. > > > > > * Note: 25% is arbitrary value and may need some tweak. > > > > > */ > > > > > - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); > > > > > - if (ret < 0) { > > > > > - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", > > > > > - aux->name, ret); > > > > > - return 0; > > > > > - } > > > > > - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); > > > > > - if (ret < 0) { > > > > > - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", > > > > > - aux->name, ret); > > > > > - return 0; > > > > > - } > > > > > - pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > > > - pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; > > > > > - > > > > > - /* Ensure frequency is within 25% of desired value */ > > > > > fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4); > > > > > fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4); > > > > > if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) { > > > > > > > > -- > > > > With best wishes > > > > Dmitry > > > > > > > > -- > > With best wishes > > Dmitry
diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c index e2439c8a7fefe116b04aaa689b557e2387b05540..fcc26cb96a51066a503433b2dc660126155d179c 100644 --- a/drivers/gpu/drm/display/drm_dp_helper.c +++ b/drivers/gpu/drm/display/drm_dp_helper.c @@ -28,6 +28,7 @@ #include <linux/init.h> #include <linux/iopoll.h> #include <linux/kernel.h> +#include <linux/minmax.h> #include <linux/module.h> #include <linux/sched.h> #include <linux/seq_file.h> @@ -4033,8 +4034,33 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf aux->name, ret); return -ENODEV; } - pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK; + + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); + if (ret != 1) { + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", + aux->name, ret); + return -ENODEV; + } + pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; + + ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); + if (ret != 1) { + drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", + aux->name, ret); + return -ENODEV; + } + pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; + + /* + * Per VESA eDP Spec v1.4b, section 3.3.10.2: + * If DP_EDP_PWMGEN_BIT_COUNT is less than DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, + * the sink must use the MIN value as the effective PWM bit count. + * Clamp the reported value to the [MIN, MAX] capability range to ensure + * correct brightness scaling on compliant eDP panels. + */ + pn = clamp(pn, pn_min, pn_max); + bl->max = (1 << pn) - 1; if (!driver_pwm_freq_hz) return 0; @@ -4054,29 +4080,15 @@ drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_inf */ fxp = DIV_ROUND_CLOSEST(1000 * DP_EDP_BACKLIGHT_FREQ_BASE_KHZ, driver_pwm_freq_hz); - /* Use highest possible value of Pn for more granularity of brightness adjustment while + /* + * Ensure frequency is within 25% of desired value. + * Use highest possible value of Pn for more granularity of brightness adjustment while * satisfying the conditions below. * - Pn is in the range of Pn_min and Pn_max * - F is in the range of 1 and 255 * - FxP is within 25% of desired value. * Note: 25% is arbitrary value and may need some tweak. */ - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min); - if (ret < 0) { - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap min: %d\n", - aux->name, ret); - return 0; - } - ret = drm_dp_dpcd_read_byte(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max); - if (ret < 0) { - drm_dbg_kms(aux->drm_dev, "%s: Failed to read pwmgen bit count cap max: %d\n", - aux->name, ret); - return 0; - } - pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK; - pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK; - - /* Ensure frequency is within 25% of desired value */ fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4); fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4); if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {