Re: [PATCH v5 05/17] drm: bridge: analogix/dp: dynamic parse sync_pol & interlace & dynamic_range

[Yakir Yang <ykk@rock-chips.com>]

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Hi Krzysztof,

On 09/30/2015 03:34 PM, Krzysztof Kozlowski wrote:
> On 30.09.2015 16:19, Yakir Yang wrote:
>> Hi Krzysztof,
>>
>> On 09/30/2015 01:32 PM, Krzysztof Kozlowski wrote:
>>> On 22.09.2015 16:37, Yakir Yang wrote:
>>>> Both hsync/vsync polarity and interlace mode can be parsed from
>>>> drm display mode, and dynamic_range and ycbcr_coeff can be judge
>>>> by the video code.
>>>>
>>>> But presumably Exynos still relies on the DT properties, so take
>>>> good use of mode_fixup() in to achieve the compatibility hacks.
>>>>
>>>> Signed-off-by: Yakir Yang <ykk@rock-chips.com>
>>>> ---
>>>> Changes in v5:
>>>> - Switch video timing type to "u32", so driver could use "of_property_read_u32"
>>>>    to get the backword timing values.
>>> Okay
>>>
>>>> Krzysztof suggest me that driver could use
>>>>    the "of_property_read_bool" to get backword timing values, but that interfacs
>>>>    would modify the original drm_display_mode timing directly (whether those
>>>>    properties exists or not).
>>> Hmm, I don't understand. You have a:
>>> 	struct video_info {
>>> 		bool h_sync_polarity;
>>> 		bool v_sync_polarity;
>>> 		bool interlaced;
>>> 	};
>>>
>>> so what is wrong with:
>>> 	dp_video_config->h_sync_polarity =
>>> 		of_property_read_bool(dp_node, "hsync-active-high");
>>>
>>> Is it exactly the same binding as previously?
>> Yes, it is the same binding as previously. But just a note that we already
>> mark those DT binding as deprecated.
>>
>> +-interlaced:            deprecated prop that can parsed frm drm_display_mode.
>> +-vsync-active-high:     deprecated prop that can parsed frm drm_display_mode.
>> +-hsync-active-high:     deprecated prop that can parsed frm drm_display_mode.
>>
>>
>> For now those values should come from "struct drm_display_mode",
>> and we already parsed them out from "drm_display_mode" before
>> driver provide the backward compatibility.
>>
>> Let's used the "hsync-active-high" example:
>>      As for now the code would like:
>>      static void analogix_dp_bridge_mode_set(...)
>>      {
>>          // Parsed timing value from "drm_display_mode"
>>          video->h_sync_polarity = !!(mode->flags & DRM_MODE_FLAG_NHSYNC);
>>
>>          // Try to detect the deprecated property, providing
>>          // the backward compatibility
>>          of_property_read_u32(dp_node, "hsync-active-high",
>>                                   &video->h_sync_polarity);
>>
>>          /*
>>           * In this case, if "hsync-active-high" property haven't been
>>           * found, then the video timing "h_sync_polarity" would  keep
>>           * no change, keeping the parsed value from "drm_display_mode"
>>           */
>>      }
>>
>>      But if keep the "of_property_read_bool", then code would like:
>>      static void analogix_dp_bridge_mode_set(...)
>>      {
>>          // Parsed timing value from "drm_display_mode"
>>          video->h_sync_polarity = !!(mode->flags & DRM_MODE_FLAG_NHSYNC);
>>
>>          // Try to detect the deprecated property, providing
>>          // the backward compatibility
>>          video->h_sync_polarity =
>>                      of_property_read_bool(dp_node, "hsync-active-high");
>>     
>>
>>          /*
>>           * In this case, if "hsync-active-high" property haven't been
>>           * found, then the video timing "h_sync_polarity" would just
>>           * modify to "false". That is the place we don't want, cause
>>           * it would always modify the timing value parsed from
>>           * "drm_display_mode"
>>           */
>>      }
>>
> OK, I see the point of overwriting values from drm_display_mode. However
> I think you changed the binding. I believe the of_property_read_u32()
> will behave differently for such DTS:
>
> exynos_dp {
> 	...
> 	hsync-active-high;
> }
>
> It will return -EOVERFLOW which means it would be broken now...

Whoops, thanks for your remind, after try that, I do see over flow error.
static void *of_find_property_value_of_size(const struct device_node *np,
                         const char *propname, u32 len)
{
         ....
         if (len > prop->length)
                 return ERR_PTR(-EOVERFLOW);
         ...
}

So I though code should be:
     if (of_property_read_bool(dp_node, "hsync-active-high"))
         video->h_sync_polarity = true;

And we can't provide full backward compatibility for this property, cause
the previous exynos_dp driver would set this timing value to "false" when
property not defined, but analogix_dp driver keep this timing value
corresponding to "drm_display_mode" when property not found.


Thanks,
- Yakir

> Best regards,
> Krzysztof
>
>
>
>
>


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