On 2019-08-26 3:14 p.m., Francis, David wrote:
> On 2019-08-26 2:05 p.m., David Francis wrote:
>>> Synaptics DP1.4 hubs (BRANCH_ID 0x90CC24) do not
>>> support virtual DPCD registers, but do support DSC.
>>> The DSC caps can be read from the physical aux,
>>> like in SST DSC. These hubs have many different
>>> DEVICE_IDs. Add a new quirk to detect this case.
>>>
>>> Cc: Lyude Paul <lyude@xxxxxxxxxx>
>>> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
>>> Signed-off-by: David Francis <David.Francis@xxxxxxx>
>>> ---
>>> drivers/gpu/drm/drm_dp_helper.c | 2 ++
>>> include/drm/drm_dp_helper.h | 7 +++++++
>>> 2 files changed, 9 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
>>> index 2cc21eff4cf3..fc39323e7d52 100644
>>> --- a/drivers/gpu/drm/drm_dp_helper.c
>>> +++ b/drivers/gpu/drm/drm_dp_helper.c
>>> @@ -1270,6 +1270,8 @@ static const struct dpcd_quirk dpcd_quirk_list[] = {
>>> { OUI(0x00, 0x10, 0xfa), DEVICE_ID_ANY, false, BIT(DP_DPCD_QUIRK_NO_PSR) },
>>> /* CH7511 seems to leave SINK_COUNT zeroed */
>>> { OUI(0x00, 0x00, 0x00), DEVICE_ID('C', 'H', '7', '5', '1', '1'), false, BIT(DP_DPCD_QUIRK_NO_SINK_COUNT) },
>>> + /* Synaptics DP1.4 MST hubs can support DSC without virtual DPCD */
>>> + { OUI(0x90, 0xCC, 0x24), DEVICE_ID_ANY, true, BIT(DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD) },
>>
>> This seems to be generic OUI for Synaptics [1]. Could this cause us to
>> cast the net too wide?
>>
>> Even if we check that it's DP_DPCD_REV >= 1.4 there's a good chance
>> Synaptics is fixing this in the future and won't require the quirk.
>>
>> [1] https://aruljohn.com/mac/vendor/Synaptics
>>
>>
>> Harry
>
> It's not pretty, but
> - Currently the net of "all Synaptics devices with rev>DP1.4" catches every device we care about and none we don't
> - If a future Synaptics device supports virtual DPCD properly, we will check for that first and never resort to the workaround (see patch 6/6)
> - We don't know any of the properties of any hypothetical future Synaptics hardware, so we can't create cases for them now
>
That's fair enough. Thanks for the explanation.
Reviewed-by: Harry Wentland <harry.wentland@xxxxxxx>
Harry
> Also, received offline review from AMD MST DSC (Non-Linux) expert Wenjing Liu, giving me permission o mark this patch
> Reviewed-by: Wenjing Liu <Wenjing.Liu@xxxxxxx>
>
>>
>>> };
>>>
>>> #undef OUI
>>> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
>>> index 8364502f92cf..a1331b08705f 100644
>>> --- a/include/drm/drm_dp_helper.h
>>> +++ b/include/drm/drm_dp_helper.h
>>> @@ -1434,6 +1434,13 @@ enum drm_dp_quirk {
>>> * The driver should ignore SINK_COUNT during detection.
>>> */
>>> DP_DPCD_QUIRK_NO_SINK_COUNT,
>>> + /**
>>> + * @DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD:
>>> + *
>>> + * The device supports MST DSC despite not supporting Virtual DPCD.
>>> + * The DSC caps can be read from the physical aux instead.
>>> + */
>>> + DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD,
>>> };
>>>
>>> /**
>
> ________________________________________
> From: Wentland, Harry <Harry.Wentland@xxxxxxx>
> Sent: August 26, 2019 3:05 PM
> To: Francis, David; dri-devel@xxxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v8 5/6] drm/dp_mst: Add new quirk for Synaptics MST hubs
>
> On 2019-08-26 2:05 p.m., David Francis wrote:
>> Synaptics DP1.4 hubs (BRANCH_ID 0x90CC24) do not
>> support virtual DPCD registers, but do support DSC.
>> The DSC caps can be read from the physical aux,
>> like in SST DSC. These hubs have many different
>> DEVICE_IDs. Add a new quirk to detect this case.
>>
>> Cc: Lyude Paul <lyude@xxxxxxxxxx>
>> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
>> Signed-off-by: David Francis <David.Francis@xxxxxxx>
>> ---
>> drivers/gpu/drm/drm_dp_helper.c | 2 ++
>> include/drm/drm_dp_helper.h | 7 +++++++
>> 2 files changed, 9 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
>> index 2cc21eff4cf3..fc39323e7d52 100644
>> --- a/drivers/gpu/drm/drm_dp_helper.c
>> +++ b/drivers/gpu/drm/drm_dp_helper.c
>> @@ -1270,6 +1270,8 @@ static const struct dpcd_quirk dpcd_quirk_list[] = {
>> { OUI(0x00, 0x10, 0xfa), DEVICE_ID_ANY, false, BIT(DP_DPCD_QUIRK_NO_PSR) },
>> /* CH7511 seems to leave SINK_COUNT zeroed */
>> { OUI(0x00, 0x00, 0x00), DEVICE_ID('C', 'H', '7', '5', '1', '1'), false, BIT(DP_DPCD_QUIRK_NO_SINK_COUNT) },
>> + /* Synaptics DP1.4 MST hubs can support DSC without virtual DPCD */
>> + { OUI(0x90, 0xCC, 0x24), DEVICE_ID_ANY, true, BIT(DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD) },
>
> This seems to be generic OUI for Synaptics [1]. Could this cause us to
> cast the net too wide?
>
> Even if we check that it's DP_DPCD_REV >= 1.4 there's a good chance
> Synaptics is fixing this in the future and won't require the quirk.
>
> [1] https://aruljohn.com/mac/vendor/Synaptics
>
> Harry
>
>> };
>>
>> #undef OUI
>> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
>> index 8364502f92cf..a1331b08705f 100644
>> --- a/include/drm/drm_dp_helper.h
>> +++ b/include/drm/drm_dp_helper.h
>> @@ -1434,6 +1434,13 @@ enum drm_dp_quirk {
>> * The driver should ignore SINK_COUNT during detection.
>> */
>> DP_DPCD_QUIRK_NO_SINK_COUNT,
>> + /**
>> + * @DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD:
>> + *
>> + * The device supports MST DSC despite not supporting Virtual DPCD.
>> + * The DSC caps can be read from the physical aux instead.
>> + */
>> + DP_DPCD_QUIRK_DSC_WITHOUT_VIRTUAL_DPCD,
>> };
>>
>> /**
>>
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