RFC: DSI host capabilities (was: [PATCH RFC 03/10] drm/panel: Add LGD panel driver for Sony Xperia XZ3)

[Neil Armstrong]

On 30/05/2023 14:36, Dmitry Baryshkov wrote:
> On 30/05/2023 15:15, AngeloGioacchino Del Regno wrote:
>> Il 30/05/23 13:44, Dmitry Baryshkov ha scritto:
>>> On Tue, 30 May 2023 at 10:24, Neil Armstrong <neil.armstrong at linaro.org> wrote:
>>>>
>>>> Hi Marijn, Dmitry, Caleb, Jessica,
>>>>
>>>> On 29/05/2023 23:11, Marijn Suijten wrote:
>>>>> On 2023-05-22 04:16:20, Dmitry Baryshkov wrote:
>>>>> <snip>
>>>>>>> +   if (ctx->dsi->dsc) {
>>>>>>
>>>>>> dsi->dsc is always set, thus this condition can be dropped.
>>>>>
>>>>> I want to leave room for possibly running the panel without DSC (at a
>>>>> lower resolution/refresh rate, or at higher power consumption if there
>>>>> is enough BW) by not assigning the pointer, if we get access to panel
>>>>> documentation: probably one of the magic commands sent in this driver
>>>>> controls it but we don't know which.
>>>>
>>>> I'd like to investigate if DSC should perhaps only be enabled if we
>>>> run non certain platforms/socs ?
>>>>
>>>> I mean, we don't know if the controller supports DSC and those particular
>>>> DSC parameters so we should probably start adding something like :
>>>>
>>>> static drm_dsc_config dsc_params_qcom = {}
>>>>
>>>> static const struct of_device_id panel_of_dsc_params[] = {
>>>>          { .compatible = "qcom,sm8150", , .data = &dsc_params_qcom },
>>>>          { .compatible = "qcom,sm8250", , .data = &dsc_params_qcom },
>>>>          { .compatible = "qcom,sm8350", , .data = &dsc_params_qcom },
>>>>          { .compatible = "qcom,sm8450", , .data = &dsc_params_qcom },
>>>> };
>>>
>>> I think this would damage the reusability of the drivers. The panel
>>> driver does not actually care if the SoC is SM8350, sunxi-something or
>>> RCar.
>>> Instead it cares about host capabilities.
>>>
>>> I think instead we should extend mipi_dsi_host:
>>>
>>> #define MIPI_DSI_HOST_MODE_VIDEO BIT(0)

I assume all DSI controller supports Video mode, so it should be a negative here
if for a reason it's not the case.

There should also be a flag to tell if sending LP commands sending while
in HS Video mode is supported.

>>> #define MIPI_DSI_HOST_MODE_CMD  BIT(1)
>>> #define MIPI_DSI_HOST_VIDEO_SUPPORTS_COMMANDS BIT(2)
>>> // FIXME: do we need to provide additional caps here ?
>>>
>>> #define MIPI_DSI_DSC_1_1 BIT(0)
>>> #define MIPI_DSI_DSC_1_2 BIT(1)
>>> #define MIPI_DSI_DSC_NATIVE_422 BIT(2)
>>> #define MIPI_DSI_DSC_NATIVE_420 BIT(3)
>>> #define MIPI_DSI_DSC_FRAC_BPP BIT(4)
>>> // etc.
>>>
>>> struct mipi_dsi_host {
>>>   // new fields only
>>>    unsigned long mode_flags;
>>>    unsigned long dsc_flags;
>>> };
>>>
>>> Then the panel driver can adapt itself to the host capabilities and
>>> (possibly) select one of the internally supported DSC profiles.
>>>
>>
>> I completely agree about extending mipi_dsi_host, other SoCs could reuse that and
>> support for DSC panels would become a lot cleaner.
> 
> Sounds good. I will wait for one or two more days (to get the possible feedback on fields/flags/etc) and post an RFC patch to dri-devel.

Good, I was waiting until a DSC panel appears on the list (and I failed to be the first), it's now the case.

For VTRD6130, the panel is capable of the 4 modes:
- video mode
- command mode
- video mode & DSC
- command mode & DSC

So it would need such info to enable one of the mode in some order to determine.

Thanks,
Neil
> 
>>
>> For example, on MediaTek DRM there's some support for DSC, more or less the same
>> for SPRD DRM and some DSI bridge drivers... having a clean infrastructure would
>> definitely help.
>>
>> I'm sad I cannot offer testing in that case because despite being sure that there
>> are MTK smartphones around with DSI panels using DSC, I have none... and all of the
>> Chromebooks are not using DSC anyway (but using DisplayPort compression, which is
>> obviously an entirely different beast).
>>
>>>>
>>>> ...
>>>> static int sony_akatsuki_lgd_probe(struct mipi_dsi_device *dsi)
>>>> ...
>>>>          const struct of_device_id *match;
>>>>
>>>> ...
>>>>          match = of_match_node(panel_of_dsc_params, of_root);
>>>>          if (match && match->data) {
>>>>                  dsi->dsc = devm_kzalloc(&dsi->dev, sizeof(*dsc), GFP_KERNEL);
>>>>                  memcpy(dsi->dsc, match->data, sizeof(*dsc));
>>>>          } else {
>>>>                  dev_warn(&dsi->dev, "DSI controller is not marked as supporting DSC\n");
>>>>          }
>>>> ...
>>>> }
>>>>
>>>> and probably bail out if it's a DSC only panel.
>>>>
>>
>> Usually DDICs support both DSC and non-DSC modes, depending on the initial
>> programming (read: init commands)... but the usual issue is that many DDICs
>> are not publicly documented for reasons, so yes, bailing out if DSC is not
>> supported would be the only option, and would be fine at this point.
>>
>> Cheers,
>> Angelo
>>
>>>> We could alternatively match on the DSI controller's dsi->host->dev instead of the SoC root compatible.
>>>>
>>>> Neil
>>>
>>
>