[PATCH] drm/mgag200: Increase bandwidth for G200se A rev1

[Thomas Zimmermann]

Am 24.07.23 um 20:48 schrieb Thomas Zimmermann:
> Hi Jocelyn
> 
> Am 17.07.23 um 15:29 schrieb Jocelyn Falempe:
>> A G200SE_A rev 1 user reported that prior to v6.0, he was able to get 
>> Xorg
>> working at 1440x900 at 60Hz. This somehow bypassed the bandwidth test in the
>> driver. After v6.0, and the driver refactor, it's no longer possible.
> 
> I took that bandwidth number from the old source code at
> 
> 
> https://elixir.bootlin.com/linux/v5.19/source/drivers/gpu/drm/mgag200/mgag200_mode.c#L725
> 
>  From this code, I don't see how it skipped this test. Maybe the 
> refactoring is incorrect.

There's a difference that might be worth investigating: if the unique 
rev equals 0x00, the current code will use the settings for rev 1.

 
https://elixir.bootlin.com/linux/v6.4/source/drivers/gpu/drm/mgag200/mgag200_g200se.c#L514

Compare this to the old code, which would have taken the settings for 
rev 3 and later:

https://elixir.bootlin.com/linux/v5.19/source/drivers/gpu/drm/mgag200/mgag200_mode.c#L719

Best regards
Thomas

> 
> Do you have the opportunity to further debug this issue on the users 
> machine?  I'd be interested in the exact model and the unique_rev_id 
> (you said A, rev1 ?) and if the early-out branches in 
> mga_vga_calculate_mode_bandwidth() are being taken. Can you figure out 
> how exactly the CPU moves through mga_vga_mode_valid().
> 
> Best regards
> Thomas
> 
>> So increase the bandwidth, as the hardware is able to do it.
>>
>> In mgag200_calculate_mode_bandwidth(), the bandwidth for 1440x900 at 60 is
>> 30318019, while 24400 * 1024 = 24985600 and 30100 * 1024 = 30822400.
>> Raising the bandwidth from 24400 to 30100 is enough to allow this mode.
>>
>> Reported-by: Roger Sewell <roger.sewell at cantab.net>
>> Tested-by: Roger Sewell <roger.sewell at cantab.net>
>> Signed-off-by: Jocelyn Falempe <jfalempe at redhat.com>
>> ---
>>   drivers/gpu/drm/mgag200/mgag200_g200se.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/mgag200/mgag200_g200se.c 
>> b/drivers/gpu/drm/mgag200/mgag200_g200se.c
>> index bd6e573c9a1a..3b49e30931e1 100644
>> --- a/drivers/gpu/drm/mgag200/mgag200_g200se.c
>> +++ b/drivers/gpu/drm/mgag200/mgag200_g200se.c
>> @@ -437,7 +437,7 @@ static int mgag200_g200se_pipeline_init(struct 
>> mga_device *mdev)
>>    */
>>   static const struct mgag200_device_info 
>> mgag200_g200se_a_01_device_info =
>> -    MGAG200_DEVICE_INFO_INIT(1600, 1200, 24400, false, 0, 1, true);
>> +    MGAG200_DEVICE_INFO_INIT(1600, 1200, 30100, false, 0, 1, true);
>>   static const struct mgag200_device_info 
>> mgag200_g200se_a_02_device_info =
>>       MGAG200_DEVICE_INFO_INIT(1920, 1200, 30100, false, 0, 1, true);
>>
>> base-commit: c2268daa65fb415cfd463016ad54c20afef8f75e
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
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