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

From: Icenowy Zheng <icenowy@aosc.io>
To: Torsten Duwe <duwe@lst.de>
Cc: Jernej Skrabec <jernej.skrabec@siol.net>,
	Jonas Karlman <jonas@kwiboo.se>,
	Neil Armstrong <narmstrong@baylibre.com>,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	Vasily Khoruzhick <anarsoul@gmail.com>,
	Andrzej Hajda <a.hajda@samsung.com>,
	Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
	Maxime Ripard <maxime@cerno.tech>
Subject: Re: [PATCH] drm/bridge: analogix-anx6345: fix set of link bandwidth
Date: Sat, 22 Feb 2020 10:43:02 +0800	[thread overview]
Message-ID: <1E7BDB0F-639B-42BB-A4B4-A4C8CF94EBE0@aosc.io> (raw)
In-Reply-To: <20200221171328.GC6928@lst.de>

于 2020年2月22日 GMT+08:00 上午1:13:28, Torsten Duwe <duwe@lst.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@aosc.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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