linux-kernel - Re: [PATCH] drm/bridge: analogix-anx6345: fix set of link bandwidth

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Message-ID: <08f290ef-7dd0-c8b9-0177-3248fb153eca@suse.de>
Date:   Thu, 27 Feb 2020 12:34:13 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Icenowy Zheng <icenowy@...c.io>, Torsten Duwe <duwe@....de>
Cc:     Jernej Skrabec <jernej.skrabec@...l.net>,
        Neil Armstrong <narmstrong@...libre.com>,
        Jonas Karlman <jonas@...boo.se>, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Maxime Ripard <maxime@...no.tech>
Subject: Re: [PATCH] drm/bridge: analogix-anx6345: fix set of link bandwidth

Hi

Am 26.02.20 um 12:02 schrieb Icenowy Zheng:
> 
> 
> 于 2020年2月26日 GMT+08:00 下午6:58:43, Thomas Zimmermann <tzimmermann@...e.de> 写到:
>> Hi Iceynow,
>>
>> Torsten asked me to merge your patch via drm-misc-next. I'd add the
>> additional cc and fixes tags that Torsten listed. Are you OK with that?
> 
> I think this fixes a driver (and a board) available in 5.6.
> 
> Maybe it should enter fixes?

Pushed to drm-misc-fixes

Best regards
Thomas

> 
>>
>> Best regards
>> Thomas
>>
>> Am 22.02.20 um 03:43 schrieb Icenowy Zheng:
>>>
>>>
>>> 于 2020年2月22日 GMT+08:00 上午1:13:28, Torsten Duwe <duwe@....de> 写到:
>>>> On Sat, Feb 22, 2020 at 12:51:27AM +0800, Icenowy Zheng wrote:
>>>>> Current code tries to store the link rate (in bps, which is a big
>>>>> number) in a u8, which surely overflow. Then it's converted back to
>>>>> bandwidth code (which is thus 0) and written to the chip.
>>>>>
>>>>> The code sometimes works because the chip will automatically
>> fallback
>>>> to
>>>>> the lowest possible DP link rate (1.62Gbps) when get the invalid
>>>> value.
>>>>> However, on the eDP panel of Olimex TERES-I, which wants 2.7Gbps
>>>> link,
>>>>> it failed.
>>>>>
>>>>> As we had already read the link bandwidth as bandwidth code in
>>>> earlier
>>>>> code (to check whether it is supported), use it when setting
>>>> bandwidth,
>>>>> instead of converting it to link rate and then converting back.
>>>>>
>>>>> Fixes: e1cff82c1097 ("drm/bridge: fix anx6345 compilation for
>> v5.5")
>>>>> Signed-off-by: Icenowy Zheng <icenowy@...c.io>
>>>>> ---
>>>>>  drivers/gpu/drm/bridge/analogix/analogix-anx6345.c | 3 +--
>>>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/bridge/analogix/analogix-anx6345.c
>>>> b/drivers/gpu/drm/bridge/analogix/analogix-anx6345.c
>>>>> index 56f55c53abfd..2dfa2fd2a23b 100644
>>>>> --- a/drivers/gpu/drm/bridge/analogix/analogix-anx6345.c
>>>>> +++ b/drivers/gpu/drm/bridge/analogix/analogix-anx6345.c
>>>>> @@ -210,8 +210,7 @@ static int anx6345_dp_link_training(struct
>>>> anx6345 *anx6345)
>>>>>  	if (err)
>>>>>  		return err;
>>>>>  
>>>>> -	dpcd[0] = drm_dp_max_link_rate(anx6345->dpcd);
>>>>> -	dpcd[0] = drm_dp_link_rate_to_bw_code(dpcd[0]);
>>>>> +	dpcd[0] = dp_bw;
>>>>
>>>> Why do you make this assignment and not use dp_bw directly in the
>> call?
>>>
>>> Because the dpcd array is then written as a continous array
>>> back to DPCD.
>>>
>>>>
>>>>>  	err = regmap_write(anx6345->map[I2C_IDX_DPTX],
>>>>>  			   SP_DP_MAIN_LINK_BW_SET_REG, dpcd[0]);
>>>>                                                       ^^^^^^
>>>>>  	if (err)
>>>>> -- 
>>>>> 2.24.1
>>>>
>>>> BTW, my version is only a bit more verbose:
>>>>
>>>> https://patchwork.freedesktop.org/patch/354344/
>>>>
>>>> 	Torsten
>>>
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer