[Intel-gfx] [RFC] drm: Do not call drm_probe_ddc() when connector force isn't specified

[Daniel Vetter]

On Thu, Jun 6, 2019 at 9:38 AM Harish Chegondi
<harish.chegondi at intel.com> wrote:
>
> This would allow the EDID override to be handled correctly in
> drm_do_get_edid() for cases where EDID data is missing or corrupt.
>
> All drm_probe_ddc() does is call drm_do_probe_ddc_edid( , , , 1)
> which probes the display by reading 1 byte of EDID data via I2C.
> This patch removes the call to drm_probe_ddc() from drm_get_edid()
> but drm_get_edid() calls drm_do_get_edid() which first handles
> the EDID override case and then calls
> drm_do_probe_ddc_edid( , , ,EDID_LENGTH) via function pointer
> argument get_edid_block. So, the display device is still being
> probed by reading EDID_LENGTH bytes of EDID data via I2C.
>
> Cc: Jani Nikula <jani.nikula at intel.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Harish Chegondi <harish.chegondi at intel.com>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=107583

Since it's a regression we need to annotate this correctly, for the
next version please include:

Fixes: 53fd40a90f3c ("drm: handle override and firmware EDID at
drm_do_get_edid() level")
Cc: <stable at vger.kernel.org> # v4.15+

So there's a pile more drm_probe_ddc calls all around in drivers, but
I reviewed them all, and they're all in ->detect callbacks. So not
affecting the regression we're discussing here. Looking at
drm_do_get_edid this should also not result in more failures. The only
thing this changes is that drm_do_get_edid will retry a bunch more
times if nothing is connected (4 times, instead of just the one probe
that drm_probe_ddc does). I guess we can restore that if anyone cares,
should at least mention it in the commit message.

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>


> ---
>  drivers/gpu/drm/drm_edid.c | 3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index d87f574feeca..41c420706532 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -1724,9 +1724,6 @@ struct edid *drm_get_edid(struct drm_connector *connector,
>         if (connector->force == DRM_FORCE_OFF)
>                 return NULL;
>
> -       if (connector->force == DRM_FORCE_UNSPECIFIED && !drm_probe_ddc(adapter))
> -               return NULL;

Trouble is there's a lot more drm_probe_ddc calls all over, and a lot of these
> -
>         edid = drm_do_get_edid(connector, drm_do_probe_ddc_edid, adapter);
>         if (edid)
>                 drm_get_displayid(connector, edid);
> --
> 2.21.0
>
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch