| Message ID | 20191015143509.1104985-7-thierry.reding@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/dp: Move drm_dp_link helpers to Tegra DRM | expand |
On Tue, 2019-10-15 at 16:35 +0200, Thierry Reding wrote: > From: Thierry Reding <treding@nvidia.com> > > Store the AUX read interval from DPCD, so that it can be used to wait > for the durations given in the specification during link training. > > Signed-off-by: Thierry Reding <treding@nvidia.com> > --- > include/drm/drm_dp_helper.h | 33 +++++++++++++++++++++++++++++++++ > 1 file changed, 33 insertions(+) > > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h > index 7a537ffc2fb1..6c12de6f7e46 100644 > --- a/include/drm/drm_dp_helper.h > +++ b/include/drm/drm_dp_helper.h > @@ -25,8 +25,11 @@ > > #include <linux/delay.h> > #include <linux/i2c.h> > +#include <linux/time64.h> > #include <linux/types.h> > > +#include <drm/drm_print.h> > + > /* > * Unless otherwise noted, all values are from the DP 1.1a spec. Note that > * DP and DPCD versions are independent. Differences from 1.0 are not > noted, > @@ -1297,6 +1300,36 @@ drm_dp_alternate_scrambler_reset_cap(const u8 > dpcd[DP_RECEIVER_CAP_SIZE]) > DP_ALTERNATE_SCRAMBLER_RESET_CAP; > } > > +/** > + * drm_dp_read_aux_interval() - read the AUX read interval from the DPCD > + * @dpcd: receiver capacity buffer > + * > + * Reads the AUX read interval (in microseconds) from the DPCD. Note that > the > + * TRAINING_AUX_RD_INTERVAL stores the value in units of 4 milliseconds. If > no > + * read interval is specified and for DPCD v1.4 and later, the read > interval > + * is always 100 microseconds. > + * > + * Returns: > + * The read AUX interval in microseconds. > + */ > +static inline unsigned int > +drm_dp_aux_rd_interval(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) > +{ > + unsigned int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] & > + DP_TRAINING_AUX_RD_MASK; > + > + if (rd_interval > 4) > + DRM_DEBUG_KMS("AUX interval %u, out of range (max: 4)\n", > + rd_interval); Do you think it might be worth clamping the value to 4 here? > + > + if (rd_interval > 0 && dpcd[DP_DPCD_REV] < DP_DPCD_REV_14) Also small nit pick: you can just use rd_interval instead of rd_interval > 0 > + rd_interval *= 4 * USEC_PER_MSEC; > + else > + rd_interval = 100; > + > + return rd_interval; > +} > + > /* > * DisplayPort AUX channel > */
On Fri, Oct 18, 2019 at 05:27:59PM -0400, Lyude Paul wrote: > On Tue, 2019-10-15 at 16:35 +0200, Thierry Reding wrote: > > From: Thierry Reding <treding@nvidia.com> > > > > Store the AUX read interval from DPCD, so that it can be used to wait > > for the durations given in the specification during link training. > > > > Signed-off-by: Thierry Reding <treding@nvidia.com> > > --- > > include/drm/drm_dp_helper.h | 33 +++++++++++++++++++++++++++++++++ > > 1 file changed, 33 insertions(+) > > > > diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h > > index 7a537ffc2fb1..6c12de6f7e46 100644 > > --- a/include/drm/drm_dp_helper.h > > +++ b/include/drm/drm_dp_helper.h > > @@ -25,8 +25,11 @@ > > > > #include <linux/delay.h> > > #include <linux/i2c.h> > > +#include <linux/time64.h> > > #include <linux/types.h> > > > > +#include <drm/drm_print.h> > > + > > /* > > * Unless otherwise noted, all values are from the DP 1.1a spec. Note that > > * DP and DPCD versions are independent. Differences from 1.0 are not > > noted, > > @@ -1297,6 +1300,36 @@ drm_dp_alternate_scrambler_reset_cap(const u8 > > dpcd[DP_RECEIVER_CAP_SIZE]) > > DP_ALTERNATE_SCRAMBLER_RESET_CAP; > > } > > > > +/** > > + * drm_dp_read_aux_interval() - read the AUX read interval from the DPCD > > + * @dpcd: receiver capacity buffer > > + * > > + * Reads the AUX read interval (in microseconds) from the DPCD. Note that > > the > > + * TRAINING_AUX_RD_INTERVAL stores the value in units of 4 milliseconds. If > > no > > + * read interval is specified and for DPCD v1.4 and later, the read > > interval > > + * is always 100 microseconds. > > + * > > + * Returns: > > + * The read AUX interval in microseconds. > > + */ > > +static inline unsigned int > > +drm_dp_aux_rd_interval(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) > > +{ > > + unsigned int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] & > > + DP_TRAINING_AUX_RD_MASK; > > + > > + if (rd_interval > 4) > > + DRM_DEBUG_KMS("AUX interval %u, out of range (max: 4)\n", > > + rd_interval); > Do you think it might be worth clamping the value to 4 here? Yeah, I think that makes sense. It might also be worth increasing the log level for this, perhaps even make it a WARN to make sure we catch it when this happens. > > + > > + if (rd_interval > 0 && dpcd[DP_DPCD_REV] < DP_DPCD_REV_14) > > Also small nit pick: you can just use rd_interval instead of rd_interval > 0 Yeah, I suppose so. I thought > 0 was making it really explicit, but I don't really mind either way. Thierry > > + rd_interval *= 4 * USEC_PER_MSEC; > > + else > > + rd_interval = 100; > > + > > + return rd_interval; > > +} > > + > > /* > > * DisplayPort AUX channel > > */ > -- > Cheers, > Lyude Paul >
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h index 7a537ffc2fb1..6c12de6f7e46 100644 --- a/include/drm/drm_dp_helper.h +++ b/include/drm/drm_dp_helper.h @@ -25,8 +25,11 @@ #include <linux/delay.h> #include <linux/i2c.h> +#include <linux/time64.h> #include <linux/types.h> +#include <drm/drm_print.h> + /* * Unless otherwise noted, all values are from the DP 1.1a spec. Note that * DP and DPCD versions are independent. Differences from 1.0 are not noted, @@ -1297,6 +1300,36 @@ drm_dp_alternate_scrambler_reset_cap(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) DP_ALTERNATE_SCRAMBLER_RESET_CAP; } +/** + * drm_dp_read_aux_interval() - read the AUX read interval from the DPCD + * @dpcd: receiver capacity buffer + * + * Reads the AUX read interval (in microseconds) from the DPCD. Note that the + * TRAINING_AUX_RD_INTERVAL stores the value in units of 4 milliseconds. If no + * read interval is specified and for DPCD v1.4 and later, the read interval + * is always 100 microseconds. + * + * Returns: + * The read AUX interval in microseconds. + */ +static inline unsigned int +drm_dp_aux_rd_interval(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) +{ + unsigned int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] & + DP_TRAINING_AUX_RD_MASK; + + if (rd_interval > 4) + DRM_DEBUG_KMS("AUX interval %u, out of range (max: 4)\n", + rd_interval); + + if (rd_interval > 0 && dpcd[DP_DPCD_REV] < DP_DPCD_REV_14) + rd_interval *= 4 * USEC_PER_MSEC; + else + rd_interval = 100; + + return rd_interval; +} + /* * DisplayPort AUX channel */