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
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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