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