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

[Ilia Mirkin]

On Wed, Mar 7, 2018 at 6:44 PM,  <matthew.s.atwood at intel.com> wrote:
> From: Matt Atwood <matthew.s.atwood at 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.
>
> Signed-off-by: Matt Atwood <matthew.s.atwood at intel.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 18 ++++++++++++++----
>  include/drm/drm_dp_helper.h     |  4 ++++
>  2 files changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index adf79be..671b823 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);
> +
> +       if(rd_interval == 0 || (dpcd[DP_DPCD_REV] & DP_REV_14))

Was this meant to be dpcd[DP_DPCD_REV] >= DP_REV_14? It doesn't appear
to be a bitmask...

Also I think you're supposed to say "if (" rather than "if(".

  -ilia