linux-kernel - Re: [PATCH v2 11/11] drm/rockchip/dsi: fix insufficient bandwidth of some panel

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Date:   Tue, 17 Jan 2017 17:31:53 +0800
From:   Chris Zhong <zyw@...k-chips.com>
To:     John Keeping <john@...anate.com>
Cc:     dianders@...omium.org, tfiga@...omium.org, heiko@...ech.de,
        yzq@...k-chips.com, mark.rutland@....com,
        devicetree@...r.kernel.org, robh+dt@...nel.org,
        galak@...eaurora.org, pawel.moll@....com, seanpaul@...omium.org,
        David Airlie <airlied@...ux.ie>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        linux-rockchip@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        Mark Yao <mark.yao@...k-chips.com>
Subject: Re: [PATCH v2 11/11] drm/rockchip/dsi: fix insufficient bandwidth of
 some panel

Hi John

On 01/16/2017 08:44 PM, John Keeping wrote:
> On Mon, 16 Jan 2017 18:08:31 +0800, Chris Zhong wrote:
>
>> Set the lanes bps to 1 / 0.9 times of pclk, the margin is not enough
>> for some panel, it will cause the screen display is not normal, so
>> increases the badnwidth to 1 / 0.8.
>>
>> Signed-off-by: Chris Zhong <zyw@...k-chips.com>
>>
>> ---
>>
>>   drivers/gpu/drm/rockchip/dw-mipi-dsi.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
>> index 9dfa73d..5a973fe 100644
>> --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
>> +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
>> @@ -501,8 +501,8 @@ static int dw_mipi_dsi_get_lane_bps(struct dw_mipi_dsi *dsi)
>>   
>>   	mpclk = DIV_ROUND_UP(dsi->mode->clock, MSEC_PER_SEC);
>>   	if (mpclk) {
>> -		/* take 1 / 0.9, since mbps must big than bandwidth of RGB */
>> -		tmp = mpclk * (bpp / dsi->lanes) * 10 / 9;
>> +		/* take 1 / 0.8, since mbps must big than bandwidth of RGB */
>> +		tmp = mpclk * (bpp / dsi->lanes) * 10 / 8;
> This and patch 9 are just hacking around the underlying problem in order
> to make particular panels work.  I'm pretty sure the actual issue is the
> use of hardcoded values when configuring the PHY, since the PHY
> parameters are specified in clock cycles but the MIPI spec requires
> absolute time durations.
>
> I posted a series addressing this a while ago, although I screwed up
> sending it so some patches were included twice and since no one
> expressed any interest I didn't post a cleaned up version.
>
> The relevant patch is here:
>
> https://patchwork.kernel.org/patch/9340193/
Thanks very much, your patches are very useful for me. It looks your 
method is correct.
And I am very confused why Mark Yao and me did not receive your patches 
before,
although we have subscribed the <linux-rockchip@...ts.infradead.org>.

In addition, could you tell me which device ware you testing with these 
mipi patches.
I going to test them these day.

Chris Zhong
>>   		if (tmp < max_mbps)
>>   			target_mbps = tmp;
>>   		else
>
>