On Tue, 10 May 2022, "Nautiyal, Ankit K" <ankit.k.nautiyal@xxxxxxxxx> wrote:
> LGTM.
>
> Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx>
Thanks for the review, pushed the lot already on Friday.
BR,
Jani.
>
> Regards,
>
> Ankit
>
> On 5/9/2022 5:33 PM, Jani Nikula wrote:
>> Introduce new opaque type struct drm_edid to encapsulate the EDID data
>> and the size allocated for it. The contents will be private to
>> drm_edid.c.
>>
>> There are a number of reasons for adding a container around struct edid:
>>
>> * struct edid is a raw blob pointer to data that usually originates
>> outside of the kernel. Its size is contained within the structure.
>>
>> * There's no way to attach meta information (such as allocated memory
>> size) to struct edid.
>>
>> * Validation of the EDID blob and its size become crucial, and it's
>> spread all over the subsystem, with varying levels of accuracy.
>>
>> * HDMI Forum has introduced an HF-EEODB extension that defines an
>> override EDID size within an EDID extension. The size allocated for an
>> EDID depends on whether the allocator understands the HF-EEODB
>> extension. Given a struct edid *, it's impossible to know how much
>> memory was actually allocated for it.
>>
>> There are also some reasons for making the container type struct
>> drm_edid opaque and private to drm_edid.c:
>>
>> * Have only one place for creating and parsing the EDID, to avoid
>> duplicating bugs.
>>
>> * Prepare for reading a pure DisplayID 2.0 from its own DDC address, and
>> adding it within the same struct drm_edid container, transparently,
>> and for all drivers.
>>
>> * With the idea that the drm_edid objects are immutable during their
>> lifetimes, it will be possible to refcount them and reduce EDID
>> copying everywhere (this is left for future work).
>>
>> Initially, just add the type. In follow-up, we'll start converting the
>> guts of drm_edid.c to use it, and finally add interfaces around it.
>>
>> Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
>> ---
>> drivers/gpu/drm/drm_edid.c | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
>> index dcef92c8887a..480fd9fbe412 100644
>> --- a/drivers/gpu/drm/drm_edid.c
>> +++ b/drivers/gpu/drm/drm_edid.c
>> @@ -1567,6 +1567,15 @@ static const struct drm_display_mode edid_4k_modes[] = {
>>
>> /*** DDC fetch and block validation ***/
>>
>> +/*
>> + * The opaque EDID type, internal to drm_edid.c.
>> + */
>> +struct drm_edid {
>> + /* Size allocated for edid */
>> + size_t size;
>> + const struct edid *edid;
>> +};
>> +
>> static int edid_extension_block_count(const struct edid *edid)
>> {
>> return edid->extensions;
--
Jani Nikula, Intel Open Source Graphics Center
