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

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

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@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@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@xxxxxxxxxx>
> > Tested-by: Roger Sewell <roger.sewell@xxxxxxxxxx>
> > Signed-off-by: Jocelyn Falempe <jfalempe@xxxxxxxxxx>
> > ---
> >   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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