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

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Message-ID: <07EED5EC-28C6-473D-B672-509F5C770479@aosc.io>
Date:   Wed, 26 Feb 2020 19:02:09 +0800
From:   Icenowy Zheng <icenowy@...c.io>
To:     Thomas Zimmermann <tzimmermann@...e.de>, Torsten Duwe <duwe@....de>
CC:     Jernej Skrabec <jernej.skrabec@...l.net>,
        Jonas Karlman <jonas@...boo.se>,
        Neil Armstrong <narmstrong@...libre.com>,
        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



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?

>
>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
>> 

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