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Message-ID: <23333ff7-3ae1-494f-7abe-62da6698fd00@redhat.com>
Date: Tue, 11 Oct 2022 09:46:16 +0200
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Subject: Re: [PATCH v4 5/5] drm/ofdrm: Support big-endian scanout buffers
To: Thomas Zimmermann <tzimmermann@suse.de>, airlied@linux.ie,
 daniel@ffwll.ch, deller@gmx.de, maxime@cerno.tech, sam@ravnborg.org,
 msuchanek@suse.de, mpe@ellerman.id.au, benh@kernel.crashing.org,
 paulus@samba.org, geert@linux-m68k.org, mark.cave-ayland@ilande.co.uk
References: <20220928105010.18880-1-tzimmermann@suse.de>
 <20220928105010.18880-6-tzimmermann@suse.de>
From: Javier Martinez Canillas <javierm@redhat.com>
In-Reply-To: <20220928105010.18880-6-tzimmermann@suse.de>
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Cc: linux-fbdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, dri-devel@lists.freedesktop.org
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Sender: "Linuxppc-dev" <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

Hello Thomas,

On 9/28/22 12:50, Thomas Zimmermann wrote:
> All DRM formats assume little-endian byte order. On big-endian systems,
> it is likely that the scanout buffer is in big endian as well. Update

You say it is likely, not always then? Does it depend on whether the Open
Firmware is BE or LE ?

[...]

> +static bool display_get_big_endian_of(struct drm_device *dev, struct device_node *of_node)
> +{
> +	bool big_endian;
> +
> +#ifdef __BIG_ENDIAN
> +	big_endian = true;
> +	if (of_get_property(of_node, "little-endian", NULL))
> +		big_endian = false;
> +#else
> +	big_endian = false;
> +	if (of_get_property(of_node, "big-endian", NULL))
> +		big_endian = true;
> +#endif
> +
> +	return big_endian;
> +}
> +

Ah, I see. The heuristic then is whether the build is BE or LE or if the Device
Tree has an explicit node defining the endianess. The patch looks good to me:

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat