[PATCH] drm: document that user-space should avoid parsing EDIDs

[Thomas Zimmermann]

Hi

Am 09.10.20 um 11:48 schrieb Thomas Zimmermann:
> Hi
> 
> Am 09.10.20 um 11:24 schrieb Simon Ser:
>> User-space should avoid parsing EDIDs for metadata already exposed via
>> other KMS interfaces and properties. For instance, user-space should not
>> try to extract a list of modes from the EDID: the kernel might mutate
>> the mode list (because of link capabilities or quirks for instance).
>>
>> Other metadata not exposed by KMS can be parsed by user-space. This
>> includes for instance monitor identification (make/model/serial) and
>> supported color-spaces.
>>
>> Signed-off-by: Simon Ser <contact at emersion.fr>
>> Suggested-by: Daniel Vetter <daniel.vetter at intel.com>
>> Cc: Daniel Vetter <daniel.vetter at intel.com>
>> Cc: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
>> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
>> ---
>>  drivers/gpu/drm/drm_connector.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
>> index 717c4e7271b0..00e58fd2d292 100644
>> --- a/drivers/gpu/drm/drm_connector.c
>> +++ b/drivers/gpu/drm/drm_connector.c
>> @@ -960,6 +960,10 @@ static const struct drm_prop_enum_list dp_colorspaces[] = {
>>   * 	drm_connector_update_edid_property(), usually after having parsed
>>   * 	the EDID using drm_add_edid_modes(). Userspace cannot change this
>>   * 	property.
>> + *
>> + * 	User-space should not parse the EDID to obtain information exposed via

One nit: the rest of the file uses 'userspace' instead of 'user-space'.

>> + * 	other KMS properties. For instance, user-space should not try to parse
>> + * 	mode lists from the EDID.
> 
> Acked-by: Thomas Zimmermann <tzimmermann at suse.de>
> 
> But this makes me wonder why the kernel exposes raw EDID in the first
> place. Wouldn't it be better to expose meaningful fields (display model,
> vendor, etc) instead?
> 
> Best regards
> Thomas
> 
>>   * DPMS:
>>   * 	Legacy property for setting the power state of the connector. For atomic
>>   * 	drivers this is only provided for backwards compatibility with existing
>>
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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