Re: [REGRESSION] VGA output with AST 2600 graphics.

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi Jocelyn,

thanks for reporting this bug.

Am 01.06.22 um 11:33 schrieb Jocelyn Falempe:
> Hi,
>
> I've found a regression in the ast driver, for AST2600 hardware.
>
> before the upstream commit f9bd00e0ea9d
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f9bd00e0ea9d9b04140aa969a9a13ad3597a1e4e 
>
>
> The ast driver handled AST 2600 chip like an AST 2500.
>
> After this commit, it uses some default values, more like the older AST 
> chip.
>
> There are a lot of places in the driver like this:
> https://elixir.bootlin.com/linux/v5.18.1/source/drivers/gpu/drm/ast/ast_post.c#L82 
>
> where it checks for (AST2300 || AST2400 || AST2500) but not for AST2600.
>
> This makes the VGA output, to be blurred and flickered with whites lines 
> on AST2600.
>
> The issue is present since v5.11
>
> For v5.11~v5.17 I propose a simple workaround (as there are no other 
> reference to AST2600 in the driver):
> --- a/drivers/gpu/drm/ast/ast_main.c
> +++ b/drivers/gpu/drm/ast/ast_main.c
> @@ -146,7 +146,8 @@ static int ast_detect_chip(struct drm_device *dev, 
> bool *need_post)
>
>       /* Identify chipset */
>       if (pdev->revision >= 0x50) {
> -        ast->chip = AST2600;
> +        /* Workaround to use the same codepath for AST2600 */
> +        ast->chip = AST2500;

The whole handling of different models in this driver is broken by 
design and needs to be replaced.  I don't have much of the affected 
hardware, so such things are going slowly. :(

For an intermediate fix, it would be better to change all tests for 
AST2500 to include AST2600 as well. There aren't too many IIRC.

Best regards
Thomas

>           drm_info(dev, "AST 2600 detected\n");
>       } else if (pdev->revision >= 0x40) {
>           ast->chip = AST2500;
>
> starting from v5.18, there is another reference to AST2600 in the code
> https://elixir.bootlin.com/linux/v5.18/source/drivers/gpu/drm/ast/ast_main.c#L212 
>
>
> So I think someone with good aspeed knowledge should review all 
> locations where there is a test for AST2500, and figure out what should 
> be done for AST2600
>
> Thanks,

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

Attachment: OpenPGP_signature
Description: OpenPGP digital signature