linux-kernel - Re: [PATCH v2] drm: tilcdc: implement palette loading for rev1

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Date:   Mon, 24 Oct 2016 13:02:03 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Jyri Sarha <jsarha@...com>
CC:     David Airlie <airlied@...ux.ie>,
        Kevin Hilman <khilman@...libre.com>,
        Michael Turquette <mturquette@...libre.com>,
        Sekhar Nori <nsekhar@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-drm <dri-devel@...ts.freedesktop.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Peter Ujfalusi <peter.ujfalusi@...com>
Subject: Re: [PATCH v2] drm: tilcdc: implement palette loading for rev1

On 24/10/16 12:47, Bartosz Golaszewski wrote:
> 2016-10-24 11:25 GMT+02:00 Jyri Sarha <jsarha@...com>:
>> On 10/24/16 11:43, Bartosz Golaszewski wrote:
>>> Revision 1 of the IP doesn't work if we don't load the palette (even
>>> if it's not used, which is the case for the RGB565 format).
>>>
>>> Add a function called from tilcdc_crtc_enable() which performs all
>>> required actions if we're dealing with a rev1 chip.
>>>
>>> Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
>>> ---
>>> v1 -> v2:
>>> - only allocate dma memory for revision 1
>>>
>>
>>
>> Is it enough to load the palette only once? What if lcdc is powered down
>> by power management in the middle?
>>
>> I think you should reinit the completion struct at least in
>> tilcdc_pm_resume(), if not in tilcdc_crtc_disable().
>>
>> Cheers,
>> Jyri
>>
> 
> Hi Jyri,
> 
> I ran the following test:
> 
> - tilcdc_crtc_enable() was called on device init
> - ran modetest -M tilcdc -s 26:800x600@...6 and quit
> - waited for the screen to go blank
> - tilcdc_crtc_disable() was called
> - ran modetest again
> - tilcdc_crtc_enable() was called again, this time without calling
> tilcdc_crtc_load_palette()
> - color bar still correctly displayed
> 
> Seems like it's only needed once.

If the power management does its job properly, the IP will get reset
when the IP is suspended. I'm quite sure it won't retain any palettes.

 Tomi



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