Re: [Intel-gfx] [PATCH] drm/dp: Correctly mask DP_TRAINING_AUX_RD_INTERVAL values for DP 1.4

Jani Nikula
2018-03-08T07:22:34Z

On Wed, 07 Mar 2018, matthew.s.atwood@intel.com wrote:
> From: Matt Atwood <matthew.s.atwood@intel.com>
>
> DP_TRAINING_AUX_RD_INTERVAL with DP 1.3 spec changed bit scheeme from 8
> bits to 7 in DPCD 0x000e. The 8th bit is used to identify extended
> receiver capabilities. For panels that use this new feature wait interval
> would be increased by 512 ms, when spec is max 16 ms. This behavior is
> described in table 2-158 of DP 1.4 spec address 0000eh.
>
> With the introduction of DP 1.4 spec main link clock recovery was
> standardized to 100 us regardless of TRAINING_AUX_RD_INTERVAL value.
>
> To avoid breaking panels that are not spec compiant we now warn on
> invalid values.
>
> V2: commit title/message, masking all 7 bits, warn on out of spec values.
> V3: commit message, make link train clock recovery follow DP 1.4 spec.
> V4: style changes
> V5: typo
>
> Signed-off-by: Matt Atwood <matthew.s.atwood@intel.com>
> ---
> drivers/gpu/drm/drm_dp_helper.c | 18 ++++++++++++++----
> include/drm/drm_dp_helper.h | 6 ++++++
> 2 files changed, 20 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index adf79be..cdb04c9 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -119,18 +119,28 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SI
> EXPORT_SYMBOL(drm_dp_get_adjust_request_pre_emphasis);
>
> void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
> - if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
> + int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] & DP_TRAINING_AUX_RD_MASK;
> +
> + if (rd_interval > 4)
> + DRM_DEBUG_KMS("AUX interval %d, out of range (max 4)", rd_interval);

\n missing.

> +
> + if (rd_interval == 0 || (dpcd[DP_DPCD_REV] >= DP_REV_14))
> udelay(100);
> else
> - mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
> + mdelay(rd_interval * 4);
> }
> EXPORT_SYMBOL(drm_dp_link_train_clock_recovery_delay);
>
> void drm_dp_link_train_channel_eq_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE]) {
> - if (dpcd[DP_TRAINING_AUX_RD_INTERVAL] == 0)
> + int rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] & DP_TRAINING_AUX_RD_MASK;
> +
> + if (rd_interval > 4)
> + DRM_DEBUG_KMS("AUX interval %d, out of range (max 4)", rd_interval);

\n missing.

> +
> + if (rd_interval == 0)
> udelay(400);
> else
> - mdelay(dpcd[DP_TRAINING_AUX_RD_INTERVAL] * 4);
> + mdelay(rd_interval * 4);
> }
> EXPORT_SYMBOL(drm_dp_link_train_channel_eq_delay);
>
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index da58a42..1269ef8 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -64,6 +64,11 @@
> /* AUX CH addresses */
> /* DPCD */
> #define DP_DPCD_REV 0x000
> +# define DP_REV_10 0x10
> +# define DP_REV_11 0x11
> +# define DP_REV_12 0x12
> +# define DP_REV_13 0x13
> +# define DP_REV_14 0x14

I am not sure what good these buy us, but if people think they're the
way to go, then so be it. Just bear in mind that per spec, "The DPCD
revision number does not necessarily match the DisplayPort version
number." so "DP_REV" doesn't actually mean *DP* revision.

BR,
Jani.

>
> #define DP_MAX_LINK_RATE 0x001
>
> @@ -118,6 +123,7 @@
> # define DP_DPCD_DISPLAY_CONTROL_CAPABLE (1 << 3) /* edp v1.2 or higher */
>
> #define DP_TRAINING_AUX_RD_INTERVAL 0x00e /* XXX 1.2? */
> +# define DP_TRAINING_AUX_RD_MASK 0x7F /* 1.3 */
>
> #define DP_ADAPTER_CAP 0x00f /* 1.2 */
> # define DP_FORCE_LOAD_SENSE_CAP (1 << 0)

--
Jani Nikula, Intel Open Source Technology Center
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