Re: [PATCH v7 10/10] drm/amd/display: Fetch the EDID from _DDC if available for eDP

[Mario Limonciello <mario.limonciello@xxxxxxx>]

On 9/19/2024 11:03, Alex Hung wrote:
> A minor comment (see inline below).
>
> Otherwise
>
> Reviewed-by: Alex Hung <alex.hung@xxxxxxx>
>
> On 2024-09-18 15:38, Mario Limonciello wrote:
> > Some manufacturers have intentionally put an EDID that differs from
> > the EDID on the internal panel on laptops.
> >
> > Attempt to fetch this EDID if it exists and prefer it over the EDID
> > that is provided by the panel. If a user prefers to use the EDID from
> > the panel, offer a DC debugging parameter that would disable this.
> >
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > ---
> >   .../amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 62 ++++++++++++++++++-
> >   drivers/gpu/drm/amd/include/amd_shared.h      |  5 ++
> >   2 files changed, 66 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c 
> > b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> > index 8f4be7a1ec45..05d3e00ecce0 100644
> > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> > @@ -23,6 +23,8 @@
> >    *
> >    */
> > +#include <acpi/video.h>
> > +
> >   #include <linux/string.h>
> >   #include <linux/acpi.h>
> >   #include <linux/i2c.h>
> > @@ -874,6 +876,60 @@ bool dm_helpers_is_dp_sink_present(struct dc_link 
> > *link)
> >       return dp_sink_present;
> >   }
> > +static int
> > +dm_helpers_probe_acpi_edid(void *data, u8 *buf, unsigned int block, 
> > size_t len)
> > +{
> > +    struct drm_connector *connector = data;
> > +    struct acpi_device *acpidev = ACPI_COMPANION(connector->dev->dev);
> > +    unsigned char start = block * EDID_LENGTH;
> > +    void *edid;
> > +    int r;
> > +
> > +    if (!acpidev)
> > +        return -ENODEV;
> > +
> > +    /* fetch the entire edid from BIOS */
> > +    r = acpi_video_get_edid(acpidev, ACPI_VIDEO_DISPLAY_LCD, -1, &edid);
> > +    if (r < 0) {
> > +        DRM_DEBUG_KMS("Failed to get EDID from ACPI: %d\n", r);
> > +        return r;
> > +    }
> > +    if (len > r || start > r || start + len > r) {
> > +        r = -EINVAL;
> > +        goto cleanup;
> > +    }
> > +
> > +    memcpy(buf, edid + start, len);
> > +    r = 0;
> > +
> > +cleanup:
> > +    kfree(edid);
> > +
> > +    return r;
> > +}
> > +
> > +static const struct drm_edid *
> > +dm_helpers_read_acpi_edid(struct amdgpu_dm_connector *aconnector)
> > +{
> > +    struct drm_connector *connector = &aconnector->base;
> > +
> > +    if (amdgpu_dc_debug_mask & DC_DISABLE_ACPI_EDID)
> > +        return NULL;
> > +
> > +    switch (connector->connector_type) {
> > +    case DRM_MODE_CONNECTOR_LVDS:
> > +    case DRM_MODE_CONNECTOR_eDP:
> > +        break;
> > +    default:
> > +        return NULL;
> > +    }
> > +
> > +    if (connector->force == DRM_FORCE_OFF)
> > +        return NULL;
> > +
> > +    return drm_edid_read_custom(connector, 
> > dm_helpers_probe_acpi_edid, connector);
> > +}
> > +
> >   enum dc_edid_status dm_helpers_read_local_edid(
> >           struct dc_context *ctx,
> >           struct dc_link *link,
> > @@ -896,7 +952,11 @@ enum dc_edid_status dm_helpers_read_local_edid(
> >        * do check sum and retry to make sure read correct edid.
> >        */
> >       do {
> > -        drm_edid = drm_edid_read_ddc(connector, ddc);
> > +        drm_edid = dm_helpers_read_acpi_edid(aconnector);
> > +        if (drm_edid)
> > +            DRM_DEBUG_KMS("Using ACPI provided EDID for %s\n", 
> > connector->name);
>
> It is better to always output a message when ACPI's EDID is used without 
> enabling any debug options. How about DRM_INFO?

Thanks, DRM_INFO makes sense for discoverability and will adjust it.

> > +        else
> > +            drm_edid = drm_edid_read_ddc(connector, ddc);
> >           drm_edid_connector_update(connector, drm_edid);
> >           aconnector->drm_edid = drm_edid;
> > diff --git a/drivers/gpu/drm/amd/include/amd_shared.h 
> > b/drivers/gpu/drm/amd/include/amd_shared.h
> > index 3f91926a50e9..1ec7c5e5249e 100644
> > --- a/drivers/gpu/drm/amd/include/amd_shared.h
> > +++ b/drivers/gpu/drm/amd/include/amd_shared.h
> > @@ -337,6 +337,11 @@ enum DC_DEBUG_MASK {
> >        * @DC_FORCE_IPS_ENABLE: If set, force enable all IPS, all the 
> > time.
> >        */
> >       DC_FORCE_IPS_ENABLE = 0x4000,
> > +    /**
> > +     * @DC_DISABLE_ACPI_EDID: If set, don't attempt to fetch EDID for
> > +     * eDP display from ACPI _DDC method.
> > +     */
> > +    DC_DISABLE_ACPI_EDID = 0x8000,
> >   };
> >   enum amd_dpm_forced_level;