| Message ID | 20211203084354.3105253-1-keescook@chromium.org (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | drm/dp: Actually read Adjust Request Post Cursor2 register | expand |
On Fri, 03 Dec 2021, Kees Cook <keescook@chromium.org> wrote: > The link_status array was not large enough to read the Adjust Request > Post Cursor2 register. Adjust the size to include it. Found with a > -Warray-bounds build: > > drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor': > drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds] > 59 | return link_status[r - DP_LANE0_1_STATUS]; > | ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~ > drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status' > 147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], > | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments") > Signed-off-by: Kees Cook <keescook@chromium.org> Using DP_ADJUST_REQUEST_POST_CURSOR2 has been deprecated since DP 1.3 published in 2014, and Tegra is the only user of drm_dp_get_adjust_request_post_cursor(). Instead of bumping the link status read size from 6 to 11 for all drivers I'd much rather see some other (maybe Tegra specific) solution to this. BR, Jani. > --- > include/drm/drm_dp_helper.h | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h > index 472dac376284..277643d2fe2c 100644 > --- a/include/drm/drm_dp_helper.h > +++ b/include/drm/drm_dp_helper.h > @@ -1517,7 +1517,15 @@ enum drm_dp_phy { > #define DP_MST_LOGICAL_PORT_0 8 > > #define DP_LINK_CONSTANT_N_VALUE 0x8000 > -#define DP_LINK_STATUS_SIZE 6 > +/* > + * DPCD registers in link_status: > + * Link Status: 0x202 through 0x204 > + * Sink Status: 0x205 > + * Adjust Request: 0x206 through 0x207 > + * Training Score: 0x208 through 0x20b > + * AR Post Cursor2: 0x20c > + */ > +#define DP_LINK_STATUS_SIZE 11 > bool drm_dp_channel_eq_ok(const u8 link_status[DP_LINK_STATUS_SIZE], > int lane_count); > bool drm_dp_clock_recovery_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
On Wed, Dec 08, 2021 at 01:19:28PM +0200, Jani Nikula wrote: > On Fri, 03 Dec 2021, Kees Cook <keescook@chromium.org> wrote: > > The link_status array was not large enough to read the Adjust Request > > Post Cursor2 register. Adjust the size to include it. Found with a > > -Warray-bounds build: > > > > drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor': > > drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds] > > 59 | return link_status[r - DP_LANE0_1_STATUS]; > > | ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~ > > drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status' > > 147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], > > | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments") > > Signed-off-by: Kees Cook <keescook@chromium.org> > > Using DP_ADJUST_REQUEST_POST_CURSOR2 has been deprecated since DP 1.3 > published in 2014, and Tegra is the only user of > drm_dp_get_adjust_request_post_cursor(). > > Instead of bumping the link status read size from 6 to 11 for all > drivers I'd much rather see some other (maybe Tegra specific) solution > to this. Hmmm... Well given this is currently non-functional on Tegra (and is an OOB memory read), how about just removing it entirely? diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 23f9073bc473..c9528aa62c9c 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -144,16 +144,6 @@ u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE], } EXPORT_SYMBOL(drm_dp_get_adjust_tx_ffe_preset); -u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], - unsigned int lane) -{ - unsigned int offset = DP_ADJUST_REQUEST_POST_CURSOR2; - u8 value = dp_link_status(link_status, offset); - - return (value >> (lane << 1)) & 0x3; -} -EXPORT_SYMBOL(drm_dp_get_adjust_request_post_cursor); - static int __8b10b_clock_recovery_delay_us(const struct drm_dp_aux *aux, u8 rd_interval) { if (rd_interval > 4) diff --git a/drivers/gpu/drm/tegra/dp.c b/drivers/gpu/drm/tegra/dp.c index 70dfb7d1dec5..bb5bfa93950f 100644 --- a/drivers/gpu/drm/tegra/dp.c +++ b/drivers/gpu/drm/tegra/dp.c @@ -559,8 +559,7 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link, drm_dp_get_adjust_request_pre_emphasis(status, i) >> DP_TRAIN_PRE_EMPHASIS_SHIFT; - adjust->post_cursor[i] = - drm_dp_get_adjust_request_post_cursor(status, i); + adjust->post_cursor[i] = 0; } } diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h index 30359e434c3f..28378db676c8 100644 --- a/include/drm/drm_dp_helper.h +++ b/include/drm/drm_dp_helper.h @@ -1528,8 +1528,6 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SI int lane); u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE], int lane); -u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], - unsigned int lane); #define DP_BRANCH_OUI_HEADER_SIZE 0xc #define DP_RECEIVER_CAP_SIZE 0xf Or maybe do a long link status read in Tegra only?
On Wed, Dec 08, 2021 at 01:19:28PM +0200, Jani Nikula wrote: > On Fri, 03 Dec 2021, Kees Cook <keescook@chromium.org> wrote: > > The link_status array was not large enough to read the Adjust Request > > Post Cursor2 register. Adjust the size to include it. Found with a > > -Warray-bounds build: > > > > drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor': > > drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds] > > 59 | return link_status[r - DP_LANE0_1_STATUS]; > > | ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~ > > drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status' > > 147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], > > | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments") > > Signed-off-by: Kees Cook <keescook@chromium.org> > > Using DP_ADJUST_REQUEST_POST_CURSOR2 has been deprecated since DP 1.3 > published in 2014, and Tegra is the only user of > drm_dp_get_adjust_request_post_cursor(). I see POST_CURSOR2 is used here too: drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c Here's a version of that for tegra (untested): diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 23f9073bc473..c9528aa62c9c 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -144,16 +144,6 @@ u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE], } EXPORT_SYMBOL(drm_dp_get_adjust_tx_ffe_preset); -u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], - unsigned int lane) -{ - unsigned int offset = DP_ADJUST_REQUEST_POST_CURSOR2; - u8 value = dp_link_status(link_status, offset); - - return (value >> (lane << 1)) & 0x3; -} -EXPORT_SYMBOL(drm_dp_get_adjust_request_post_cursor); - static int __8b10b_clock_recovery_delay_us(const struct drm_dp_aux *aux, u8 rd_interval) { if (rd_interval > 4) diff --git a/drivers/gpu/drm/tegra/dp.c b/drivers/gpu/drm/tegra/dp.c index 70dfb7d1dec5..f5535eb04c6b 100644 --- a/drivers/gpu/drm/tegra/dp.c +++ b/drivers/gpu/drm/tegra/dp.c @@ -549,6 +549,15 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link, { struct drm_dp_link_train_set *adjust = &link->train.adjust; unsigned int i; + u8 post_cursor; + int err; + + err = drm_dp_dpcd_read(link->aux, DP_ADJUST_REQUEST_POST_CURSOR2, + &post_cursor, sizeof(post_cursor)); + if (err < 0) { + DRM_ERROR("failed to read post_cursor2: %d\n", err); + post_cursor = 0; + } for (i = 0; i < link->lanes; i++) { adjust->voltage_swing[i] = @@ -560,7 +569,7 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link, DP_TRAIN_PRE_EMPHASIS_SHIFT; adjust->post_cursor[i] = - drm_dp_get_adjust_request_post_cursor(status, i); + (post_cursor >> (i << 1)) & 0x3; } } diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h index 30359e434c3f..28378db676c8 100644 --- a/include/drm/drm_dp_helper.h +++ b/include/drm/drm_dp_helper.h @@ -1528,8 +1528,6 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SI int lane); u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE], int lane); -u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], - unsigned int lane); #define DP_BRANCH_OUI_HEADER_SIZE 0xc #define DP_RECEIVER_CAP_SIZE 0xf Is that the right way to go?
On 2021-12-09 01:23, Kees Cook wrote: > On Wed, Dec 08, 2021 at 01:19:28PM +0200, Jani Nikula wrote: >> On Fri, 03 Dec 2021, Kees Cook <keescook@chromium.org> wrote: >>> The link_status array was not large enough to read the Adjust Request >>> Post Cursor2 register. Adjust the size to include it. Found with a >>> -Warray-bounds build: >>> >>> drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor': >>> drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds] >>> 59 | return link_status[r - DP_LANE0_1_STATUS]; >>> | ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~ >>> drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status' >>> 147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], >>> | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >>> >>> Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments") >>> Signed-off-by: Kees Cook <keescook@chromium.org> >> >> Using DP_ADJUST_REQUEST_POST_CURSOR2 has been deprecated since DP 1.3 >> published in 2014, and Tegra is the only user of >> drm_dp_get_adjust_request_post_cursor(). > > I see POST_CURSOR2 is used here too: > > drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c > Looks like we read and parse that in the admgpu driver without using drm_dp_get_adjust_request_post_cursor. I don't have a strong feeling but I liked your original patch a bit better. I'm not sure what it means when part of a spec is deprecated. Once a spec is written display vendors might implement it. We should make sure that displays like that are always handled in a sane manner. Harry > Here's a version of that for tegra (untested): > > > diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c > index 23f9073bc473..c9528aa62c9c 100644 > --- a/drivers/gpu/drm/drm_dp_helper.c > +++ b/drivers/gpu/drm/drm_dp_helper.c > @@ -144,16 +144,6 @@ u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE], > } > EXPORT_SYMBOL(drm_dp_get_adjust_tx_ffe_preset); > > -u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], > - unsigned int lane) > -{ > - unsigned int offset = DP_ADJUST_REQUEST_POST_CURSOR2; > - u8 value = dp_link_status(link_status, offset); > - > - return (value >> (lane << 1)) & 0x3; > -} > -EXPORT_SYMBOL(drm_dp_get_adjust_request_post_cursor); > - > static int __8b10b_clock_recovery_delay_us(const struct drm_dp_aux *aux, u8 rd_interval) > { > if (rd_interval > 4) > diff --git a/drivers/gpu/drm/tegra/dp.c b/drivers/gpu/drm/tegra/dp.c > index 70dfb7d1dec5..f5535eb04c6b 100644 > --- a/drivers/gpu/drm/tegra/dp.c > +++ b/drivers/gpu/drm/tegra/dp.c > @@ -549,6 +549,15 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link, > { > struct drm_dp_link_train_set *adjust = &link->train.adjust; > unsigned int i; > + u8 post_cursor; > + int err; > + > + err = drm_dp_dpcd_read(link->aux, DP_ADJUST_REQUEST_POST_CURSOR2, > + &post_cursor, sizeof(post_cursor)); > + if (err < 0) { > + DRM_ERROR("failed to read post_cursor2: %d\n", err); > + post_cursor = 0; > + } > > for (i = 0; i < link->lanes; i++) { > adjust->voltage_swing[i] = > @@ -560,7 +569,7 @@ static void drm_dp_link_get_adjustments(struct drm_dp_link *link, > DP_TRAIN_PRE_EMPHASIS_SHIFT; > > adjust->post_cursor[i] = > - drm_dp_get_adjust_request_post_cursor(status, i); > + (post_cursor >> (i << 1)) & 0x3; > } > } > > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h > index 30359e434c3f..28378db676c8 100644 > --- a/include/drm/drm_dp_helper.h > +++ b/include/drm/drm_dp_helper.h > @@ -1528,8 +1528,6 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SI > int lane); > u8 drm_dp_get_adjust_tx_ffe_preset(const u8 link_status[DP_LINK_STATUS_SIZE], > int lane); > -u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], > - unsigned int lane); > > #define DP_BRANCH_OUI_HEADER_SIZE 0xc > #define DP_RECEIVER_CAP_SIZE 0xf > > > Is that the right way to go? >
On Thu, Dec 09, 2021 at 05:20:45PM -0500, Harry Wentland wrote: > > > On 2021-12-09 01:23, Kees Cook wrote: > > On Wed, Dec 08, 2021 at 01:19:28PM +0200, Jani Nikula wrote: > >> On Fri, 03 Dec 2021, Kees Cook <keescook@chromium.org> wrote: > >>> The link_status array was not large enough to read the Adjust Request > >>> Post Cursor2 register. Adjust the size to include it. Found with a > >>> -Warray-bounds build: > >>> > >>> drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor': > >>> drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds] > >>> 59 | return link_status[r - DP_LANE0_1_STATUS]; > >>> | ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~ > >>> drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status' > >>> 147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], > >>> | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >>> > >>> Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments") > >>> Signed-off-by: Kees Cook <keescook@chromium.org> > >> > >> Using DP_ADJUST_REQUEST_POST_CURSOR2 has been deprecated since DP 1.3 > >> published in 2014, and Tegra is the only user of > >> drm_dp_get_adjust_request_post_cursor(). > > > > I see POST_CURSOR2 is used here too: > > > > drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c > > > > Looks like we read and parse that in the admgpu driver without > using drm_dp_get_adjust_request_post_cursor. Right, and probably that could be switched to use it, but I'm not sure what the impact of the larger link_status read is. > > I don't have a strong feeling but I liked your original > patch a bit better. I'm not sure what it means when part > of a spec is deprecated. Once a spec is written display > vendors might implement it. We should make sure that > displays like that are always handled in a sane manner. Jani, Dave, any guidance here? I'm fine with whatever, but the current code is for sure broken. ;) -Kees
On Thu, 09 Dec 2021, Kees Cook <keescook@chromium.org> wrote: > On Thu, Dec 09, 2021 at 05:20:45PM -0500, Harry Wentland wrote: >> >> >> On 2021-12-09 01:23, Kees Cook wrote: >> > On Wed, Dec 08, 2021 at 01:19:28PM +0200, Jani Nikula wrote: >> >> On Fri, 03 Dec 2021, Kees Cook <keescook@chromium.org> wrote: >> >>> The link_status array was not large enough to read the Adjust Request >> >>> Post Cursor2 register. Adjust the size to include it. Found with a >> >>> -Warray-bounds build: >> >>> >> >>> drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor': >> >>> drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds] >> >>> 59 | return link_status[r - DP_LANE0_1_STATUS]; >> >>> | ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~ >> >>> drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status' >> >>> 147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], >> >>> | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >> >>> >> >>> Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments") >> >>> Signed-off-by: Kees Cook <keescook@chromium.org> >> >> >> >> Using DP_ADJUST_REQUEST_POST_CURSOR2 has been deprecated since DP 1.3 >> >> published in 2014, and Tegra is the only user of >> >> drm_dp_get_adjust_request_post_cursor(). >> > >> > I see POST_CURSOR2 is used here too: >> > >> > drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c >> > >> >> Looks like we read and parse that in the admgpu driver without >> using drm_dp_get_adjust_request_post_cursor. > > Right, and probably that could be switched to use it, but I'm not sure > what the impact of the larger link_status read is. > >> >> I don't have a strong feeling but I liked your original >> patch a bit better. I'm not sure what it means when part >> of a spec is deprecated. Once a spec is written display >> vendors might implement it. We should make sure that >> displays like that are always handled in a sane manner. > > Jani, Dave, any guidance here? I'm fine with whatever, but the current > code is for sure broken. ;) Post Cursor2 was completely optional for the transmitter even before it was deprecated. And now we'd be adding 5 bytes extra to all link status reads. To fix the only user of drm_dp_get_adjust_request_post_cursor() that apparently has never worked as intended. I'm just not convinced. I was trying to look through the implications of DP_LINK_STATUS_SIZE increase, and at least drm_dp_dpcd_read_phy_link_status() comes across as something probably needing attention. BR, Jani.
On Fri, Dec 10, 2021 at 12:06:20PM +0200, Jani Nikula wrote: > On Thu, 09 Dec 2021, Kees Cook <keescook@chromium.org> wrote: > > On Thu, Dec 09, 2021 at 05:20:45PM -0500, Harry Wentland wrote: > >> > >> > >> On 2021-12-09 01:23, Kees Cook wrote: > >> > On Wed, Dec 08, 2021 at 01:19:28PM +0200, Jani Nikula wrote: > >> >> On Fri, 03 Dec 2021, Kees Cook <keescook@chromium.org> wrote: > >> >>> The link_status array was not large enough to read the Adjust Request > >> >>> Post Cursor2 register. Adjust the size to include it. Found with a > >> >>> -Warray-bounds build: > >> >>> > >> >>> drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor': > >> >>> drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds] > >> >>> 59 | return link_status[r - DP_LANE0_1_STATUS]; > >> >>> | ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~ > >> >>> drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status' > >> >>> 147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], > >> >>> | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >> >>> > >> >>> Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments") > >> >>> Signed-off-by: Kees Cook <keescook@chromium.org> > >> >> > >> >> Using DP_ADJUST_REQUEST_POST_CURSOR2 has been deprecated since DP 1.3 > >> >> published in 2014, and Tegra is the only user of > >> >> drm_dp_get_adjust_request_post_cursor(). > >> > > >> > I see POST_CURSOR2 is used here too: > >> > > >> > drivers/gpu/drm/amd/display/dc/core/dc_link_dp.c > >> > > >> > >> Looks like we read and parse that in the admgpu driver without > >> using drm_dp_get_adjust_request_post_cursor. > > > > Right, and probably that could be switched to use it, but I'm not sure > > what the impact of the larger link_status read is. > > > >> > >> I don't have a strong feeling but I liked your original > >> patch a bit better. I'm not sure what it means when part > >> of a spec is deprecated. Once a spec is written display > >> vendors might implement it. We should make sure that > >> displays like that are always handled in a sane manner. > > > > Jani, Dave, any guidance here? I'm fine with whatever, but the current > > code is for sure broken. ;) > > Post Cursor2 was completely optional for the transmitter even before it > was deprecated. > > And now we'd be adding 5 bytes extra to all link status reads. To fix > the only user of drm_dp_get_adjust_request_post_cursor() that apparently > has never worked as intended. I'm just not convinced. > > I was trying to look through the implications of DP_LINK_STATUS_SIZE > increase, and at least drm_dp_dpcd_read_phy_link_status() comes across > as something probably needing attention. Okay, it sounds like you'd prefer the "make it tegra-specific" patch I proposed. I will work that up as a proper patch and send it. Thanks!
On Fri, 10 Dec 2021, Kees Cook <keescook@chromium.org> wrote: > On Fri, Dec 10, 2021 at 12:06:20PM +0200, Jani Nikula wrote: >> Post Cursor2 was completely optional for the transmitter even before it >> was deprecated. >> >> And now we'd be adding 5 bytes extra to all link status reads. To fix >> the only user of drm_dp_get_adjust_request_post_cursor() that apparently >> has never worked as intended. I'm just not convinced. >> >> I was trying to look through the implications of DP_LINK_STATUS_SIZE >> increase, and at least drm_dp_dpcd_read_phy_link_status() comes across >> as something probably needing attention. > > Okay, it sounds like you'd prefer the "make it tegra-specific" patch I > proposed. I will work that up as a proper patch and send it. Yes. Of course, I'd like to hear Thierry's view as well. BR, Jani.
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h index 472dac376284..277643d2fe2c 100644 --- a/include/drm/drm_dp_helper.h +++ b/include/drm/drm_dp_helper.h @@ -1517,7 +1517,15 @@ enum drm_dp_phy { #define DP_MST_LOGICAL_PORT_0 8 #define DP_LINK_CONSTANT_N_VALUE 0x8000 -#define DP_LINK_STATUS_SIZE 6 +/* + * DPCD registers in link_status: + * Link Status: 0x202 through 0x204 + * Sink Status: 0x205 + * Adjust Request: 0x206 through 0x207 + * Training Score: 0x208 through 0x20b + * AR Post Cursor2: 0x20c + */ +#define DP_LINK_STATUS_SIZE 11 bool drm_dp_channel_eq_ok(const u8 link_status[DP_LINK_STATUS_SIZE], int lane_count); bool drm_dp_clock_recovery_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
The link_status array was not large enough to read the Adjust Request Post Cursor2 register. Adjust the size to include it. Found with a -Warray-bounds build: drivers/gpu/drm/drm_dp_helper.c: In function 'drm_dp_get_adjust_request_post_cursor': drivers/gpu/drm/drm_dp_helper.c:59:27: error: array subscript 10 is outside array bounds of 'const u8[6]' {aka 'const unsigned char[6]'} [-Werror=array-bounds] 59 | return link_status[r - DP_LANE0_1_STATUS]; | ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~ drivers/gpu/drm/drm_dp_helper.c:147:51: note: while referencing 'link_status' 147 | u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE], | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Fixes: 79465e0ffeb9 ("drm/dp: Add helper to get post-cursor adjustments") Signed-off-by: Kees Cook <keescook@chromium.org> --- include/drm/drm_dp_helper.h | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)