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

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Hi Krzysztof,

On 09/30/2015 04:26 PM, Krzysztof Kozlowski wrote:
On 30.09.2015 17:20, Yakir Yang wrote:
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@xxxxxxxxxxxxxx>
---
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;
Looks good.

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.
Indeed, the behaviour changes. I don't know if this is important issue...

Hmm... as I know the timing polarity would influence something like:
    - CTS test
    - HDCP function

But I though it's more likely that driver would made those functions failed if
hard code the timing polarity.

And I think it would be better to get timing polarity from "drm_display_mode".
Caused the analogix_dp driver have called the drm_add_edid_modes() that
function would parse the EDID "detailed timing" block which contained the
correct timing message that panel request.

Besides I see the exynos_fmid driver already setup the timing polarity from
"drm_display_mode", and there is no doubt that exynos dp should set the
same polarity with fmid driver (I guess, just notice that fmid is a kind of CTRC
driver).

That's to say parsing timing polarity dynamically would give more chances to
make those functions works.

Thanks,
- Yakir

Best regards,
Krzysztof




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