linux-kernel - Re: [EXT] Re: [v1] drm/arm/mali-dp: Disable checking for required pixel clock rate

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Date:   Thu, 16 May 2019 11:45:16 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Wen He <wen.he_1@....com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "liviu.dudau@....com" <liviu.dudau@....com>
Cc:     Leo Li <leoyang.li@....com>
Subject: Re: [EXT] Re: [v1] drm/arm/mali-dp: Disable checking for required
 pixel clock rate

On 16/05/2019 10:42, Wen He wrote:
> 
> 
>> -----Original Message-----
>> From: Robin Murphy [mailto:robin.murphy@....com]
>> Sent: 2019年5月16日 1:14
>> To: Wen He <wen.he_1@....com>; dri-devel@...ts.freedesktop.org;
>> linux-kernel@...r.kernel.org; liviu.dudau@....com
>> Cc: Leo Li <leoyang.li@....com>
>> Subject: [EXT] Re: [v1] drm/arm/mali-dp: Disable checking for required pixel
>> clock rate
>>
>> Caution: EXT Email
>>
>> On 15/05/2019 03:42, Wen He wrote:
>>> Disable checking for required pixel clock rate if ARCH_LAYERSCPAE is
>>> enable.
>>>
>>> Signed-off-by: Alison Wang <alison.wang@....com>
>>> Signed-off-by: Wen He <wen.he_1@....com>
>>> ---
>>> change in description:
>>>        - This check that only supported one pixel clock required clock rate
>>>        compare with dts node value. but we have supports 4 pixel clock
>>>        for ls1028a board.
>>>    drivers/gpu/drm/arm/malidp_crtc.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/arm/malidp_crtc.c
>>> b/drivers/gpu/drm/arm/malidp_crtc.c
>>> index 56aad288666e..bb79223d9981 100644
>>> --- a/drivers/gpu/drm/arm/malidp_crtc.c
>>> +++ b/drivers/gpu/drm/arm/malidp_crtc.c
>>> @@ -36,11 +36,13 @@ static enum drm_mode_status
>>> malidp_crtc_mode_valid(struct drm_crtc *crtc,
>>>
>>>        if (req_rate) {
>>>                rate = clk_round_rate(hwdev->pxlclk, req_rate);
>>> +#ifndef CONFIG_ARCH_LAYERSCAPE
>>
>> What about multiplatform builds? The kernel config doesn't tell you what
>> hardware you're actually running on.
>>
> 
> Hi Robin,
> 
> Thanks for your reply.
> 
> In fact, Only one platform integrates this IP when CONFIG_ARCH_LAYERSCAPE is set.
> Although this are not good ways, but I think it won't be a problem under multiplatform builds.

My point is that ARCH_LAYERSCAPE is going to be enabled in distribution 
kernels along with everything else, so you're effectively removing this 
check for all other vendors' Mali-DP implementations as well, which is 
probably not OK.

Furthermore, if LS1028A really only supports 4 specific modes as the BSP 
documentation I found claims, then surely you'd want a *more* specific 
check here, rather than no check at all?

Robin.