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Subject: Re: [PATCH] drm/bridge: analogix-anx6345: fix set of link bandwidth
To:     Icenowy Zheng <icenowy@aosc.io>, 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>
References: <20200221165127.813325-1-icenowy@aosc.io>
 <20200221171328.GC6928@lst.de> <1E7BDB0F-639B-42BB-A4B4-A4C8CF94EBE0@aosc.io>
From:   Thomas Zimmermann <tzimmermann@suse.de>
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Message-ID: <f4109d23-4591-1c52-2822-0a2ba358fe1f@suse.de>
Date:   Wed, 26 Feb 2020 11:58:43 +0100
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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?

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@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
> 

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