linux-kernel - Re: [PATCH] drm/mgag200: fix big-endian support

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Message-ID: <9b491299-1e56-498a-bdfb-20f2cd108280@suse.de>
Date: Wed, 3 Dec 2025 10:42:01 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: René Rebe <rene@...ctco.de>,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc: Dave Airlie <airlied@...hat.com>
Subject: Re: [PATCH] drm/mgag200: fix big-endian support

Hi,

let's first go through the ast patch. Most of that review also applies 
to this driver.

Best regards
Thomas

Am 02.12.25 um 16:42 schrieb René Rebe:
> Unlike the original deleted Matrox mga driver, the new mgag200 driver
> has the frame-buffer RGBX swapped on big-endian RISC systems. Fix by
> enabling byte swapping "PowerPC" OPMODE for any __BIG_ENDIAN config.
>
> Fixes: 414c45310625 ("mgag200: initial g200se driver (v2)")
> Signed-off-by: René Rebe <rene@...ctco.de>
> ---
> Tested on IBM 43p Model 150 (7043-150) running T2/Linux.
> ---
>   drivers/gpu/drm/mgag200/mgag200_mode.c | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
>
> diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
> index 951d715dea30..9073063f6473 100644
> --- a/drivers/gpu/drm/mgag200/mgag200_mode.c
> +++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
> @@ -655,6 +655,20 @@ void mgag200_crtc_helper_atomic_enable(struct drm_crtc *crtc, struct drm_atomic_
>   	else
>   		mgag200_crtc_fill_gamma(mdev, format);
>   
> +#ifdef __BIG_ENDIAN
> +	/* Big-endian byte-swapping */
> +	switch (format->format) {
> +	case DRM_FORMAT_RGB565:
> +		WREG32(MGAREG_OPMODE, 1 << 16);
> +		break;
> +	case DRM_FORMAT_XRGB8888:
> +		WREG32(MGAREG_OPMODE, 2 << 16);
> +		break;
> +	default:
> +		break;
> +	}
> +#endif
> +
>   	mgag200_enable_display(mdev);
>   }
>   

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)