linux-kernel - Re: [PATCH v3] drm/bridge/synopsys: dsi: add optional pixel clock

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Message-ID: <35d72e79-7200-dec7-2b53-a672f1c02b3b@st.com>
Date:   Thu, 25 Jan 2018 11:34:51 +0000
From:   Philippe CORNU <philippe.cornu@...com>
To:     Brian Norris <briannorris@...omium.org>
CC:     Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Bhumika Goyal <bhumirks@...il.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sandy Huang <hjc@...k-chips.com>,
        Heiko Stubner <heiko@...ech.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-rockchip@...ts.infradead.org" 
        <linux-rockchip@...ts.infradead.org>,
        Yannick FERTRE <yannick.fertre@...com>,
        Vincent ABRIOU <vincent.abriou@...com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Ludovic BARRE <ludovic.barre@...com>,
        Mickael REULIER <mickael.reulier@...com>,
        "hl@...k-chips.com" <hl@...k-chips.com>,
        "Chris Zhong" <zyw@...k-chips.com>,
        "nickey.yang@...k-chips.com" <nickey.yang@...k-chips.com>
Subject: Re: [PATCH v3] drm/bridge/synopsys: dsi: add optional pixel clock

Hi Brian,

On 01/24/2018 07:09 PM, Brian Norris wrote:
> On Wed, Jan 24, 2018 at 09:24:06AM +0000, Philippe CORNU wrote:
>> On 01/23/2018 09:49 PM, Brian Norris wrote:
>>> On Tue, Jan 23, 2018 at 06:08:06PM +0100, Philippe Cornu wrote:
>>>> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
>>>> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> 
>>>> @@ -828,6 +833,14 @@ __dw_mipi_dsi_probe(struct platform_device *pdev,
>>>>    		return ERR_PTR(ret);
>>>>    	}
>>>>    
>>>> +	dsi->px_clk = devm_clk_get(dev, "px_clk");
>>>
>>> Did you write a device tree binding document update for this anywhere?
>>
>> Many thanks for your review,
>>
>> yes, "px_clk" is already documented, please have a look to
>> Documentation/devicetree/bindings/display/bridge/dw_mipi_dsi.txt
> 
> Ah, I see. Normally I expect that the binding document is sent around
> when the first user of it shows up, but I guess that's not a
> requirement. Sorry I missed that!
> 
> Just a note: I don't think that Rockchip systems have an equivalent
> clock from which to directly derive the pixel clock rate. I believe it's
> controlled through additional dividers that are not part of the common
> clock framework. So this isn't particularly useful for them.
> 
> I don't think it's worth very much in this case, but:
> 
> Reviewed-by: Brian Norris <briannorris@...omium.org>
> 

Many thanks for the review and your comments.

Looking more deeply into the rockchip vop driver (in order to understand 
how the px clock is used), I can see that adjusted_mode/mode_fixup is 
(now) used.

I have already tried to use adjusted_mode/mode_fixup on stm32 but 
without success.

Nevertheless, I will do more tests with adjusted_mode/mode_fixup as it 
could help to have a simpler patch than adding the px_clk.

Many thanks,
Philippe :-)