Re: [PATCH v2 2/5] drm/tegra: Add plane support

[Mark Zhang <nvmarkzhang-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 01/15/2013 06:50 PM, Lucas Stach wrote:
> Am Dienstag, den 15.01.2013, 17:53 +0800 schrieb Mark Zhang:
>> On 01/15/2013 12:05 AM, Thierry Reding wrote:
>>> Add support for the B and C planes which support RGB and YUV pixel
>>> formats and can be used as overlays or hardware cursor.
>>
>> I think "hardware cursor" has specific meaning for Tegra(e.g: Tegra30
>> has a 32x32 24bpp or 64x64 2bpp hardware cursor). So you may change it
>> to "hardware accelerated cursor"?
>>
> According to the TRM no Tegra has ARGB hardware cursor support, but only
> 2-color. So we talked about doing the hardware cursor by using a plane.
> If the TRM is wrong in this regard and we can get a ARGB cursor on Tegra
> 3 it would be nice to know.
> 

Lucas, yes, TRM says "Hardware cursor is supported for 32x32 or for
64x64 2-bpp cursor.", but just as you can see, we can set cursor's
foreground & background color by register "DC_DISP_CURSOR_FOREGROUND_0
" & "DC_DISP_CURSOR_BACKGROUND_0".

So I asked the expert in nvidia and here is the explanation of the
hardware cursor:

"each pixel in the cursor is encoded by 2 bits.
only 3 values are used per pixel: transparent, foreground, background.

when pixel is transparent - no pixel is displayed. (also known as a mask)
when pixel is foreground - color of pixel is 24-bit value in
DC_DISP_CURSOR_FOREGROUND_0.
when pixel is background - color of pixel is 24-bit value in
DC_DISP_CURSOR_BACKGROUND_0.

So I would still phrase it as a 2-bit cursor. It's a palette with 2
colors plus a 1-bit alpha. The palette entries are 24-bit."

Mark
>>>
>>> Signed-off-by: Thierry Reding <thierry.reding-RM9K5IK7kjKj5M59NBduVrNAH6kLmebB@public.gmane.org>
>>> ---
>> [...]
>>> +};
>>> +
>>> +static int tegra_dc_add_planes(struct drm_device *drm, struct tegra_dc *dc)
>>> +{
>>> +	unsigned int i;
>>> +	int err = 0;
>>> +
>>> +	for (i = 0; i < 2; i++) {
>>> +		struct tegra_plane *plane;
>>> +
>>> +		plane = devm_kzalloc(drm->dev, sizeof(*plane), GFP_KERNEL);
>>> +		if (!plane)
>>> +			return -ENOMEM;
>>> +
>>> +		plane->index = i;
>>
>> I suggest to change this line to: "plane->index = i + 1;". This makes
>> the plane's index be consistent with Tegra's windows number. And also we
>> don't need to worry about passing "plane->index + 1" to some functions
>> which need to know which window is operating on.
>>
> Again, if we make WIN_C the root window, we can keep the plane index
> assignment as is and get rid of the "index + 1" passing.
> 
>