linux-kernel - Re: [PATCH V3] drm/mgag200: Fix big-endian support

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Message-ID: <d81983aa-05ae-43d6-82c8-d1b80cdff0a6@suse.de>
Date: Mon, 8 Dec 2025 14:21:05 +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 V3] drm/mgag200: Fix big-endian support

Hi

Am 08.12.25 um 14:18 schrieb René Rebe:
> Unlike the original, deleted Matrox mga driver, the new mgag200 driver
> has the XRGB frame-buffer byte 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>
> Cc: stable@...nel.org

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

Thanks again for the patch. I'll get it into upstream ASAP

Best regards
Thomas

> ---
> V3: move to func, mask prev reg content
> V2: move to atomic_update
> V3 was only compile tested, while V1/2 were tested on IBM 43p w/ T2/Linux.
> ---
>   drivers/gpu/drm/mgag200/mgag200_mode.c | 24 ++++++++++++++++++++++++
>   1 file changed, 24 insertions(+)
>
> diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
> index 951d715dea30..191037ce1029 100644
> --- a/drivers/gpu/drm/mgag200/mgag200_mode.c
> +++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
> @@ -161,6 +161,29 @@ static void mgag200_set_startadd(struct mga_device *mdev,
>   	WREG_ECRT(0x00, crtcext0);
>   }
>   
> +/*
> + * Set the opmode for the hardware swapper for Big-Endian processor
> + * support for the frame buffer aperture and DMAWIN space.
> + */
> +static void mgag200_set_datasiz(struct mga_device *mdev, u32 format)
> +{
> +#if __BIG_ENDIAN
> +	u32 opmode = RREG32(MGAREG_OPMODE);
> +	opmode &= ~(GENMASK(17, 16) | GENMASK(9, 8) | GENMASK(3, 2));
> +
> +	/* Big-endian byte-swapping */
> +	switch (format) {
> +	case DRM_FORMAT_RGB565:
> +		opmode |= 0x10100;
> +		break;
> +	case DRM_FORMAT_XRGB8888:
> +		opmode |= 0x20200;
> +		break;
> +	}
> +	WREG32(MGAREG_OPMODE, opmode);
> +#endif
> +}
> +
>   void mgag200_init_registers(struct mga_device *mdev)
>   {
>   	u8 crtc11, misc;
> @@ -496,6 +519,7 @@ void mgag200_primary_plane_helper_atomic_update(struct drm_plane *plane,
>   	struct drm_atomic_helper_damage_iter iter;
>   	struct drm_rect damage;
>   
> +	mgag200_set_datasiz(mdev, fb->format->format);
>   	drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
>   	drm_atomic_for_each_plane_damage(&iter, &damage) {
>   		mgag200_handle_damage(mdev, shadow_plane_state->data, fb, &damage);

-- 
--
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)