[PATCH] drm: hdlcd: Work properly in big-endian mode

[liviu.dudau at arm.com]

On Wed, Dec 07, 2016 at 03:31:40PM +0000, Robin Murphy wrote:
> Under a big-endian kernel, colours on the framebuffer all come out a
> delightful shade of wrong, 

So you are saying that wrong is only a 1 bit value?


> since we fail to take the reversed byte
> order into account. Fortunately, the HDLCD has a control bit to make it
> automatically byteswap big-endian data; let's use it as appropriate.
> 
> Signed-off-by: Robin Murphy <robin.murphy at arm.com>

Change looks good to me, but as Daniel has mentioned, we should have failed
the modesetting as the buffer we are passed should be in the wrong fourcc format.

Any way I can play with a big-endian filesystem that you can share?

Best regards,
Liviu

> ---
>  drivers/gpu/drm/arm/hdlcd_crtc.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/arm/hdlcd_crtc.c b/drivers/gpu/drm/arm/hdlcd_crtc.c
> index 28341b32067f..eceb7bed5dd0 100644
> --- a/drivers/gpu/drm/arm/hdlcd_crtc.c
> +++ b/drivers/gpu/drm/arm/hdlcd_crtc.c
> @@ -63,6 +63,7 @@ static int hdlcd_set_pxl_fmt(struct drm_crtc *crtc)
>  	uint32_t pixel_format;
>  	struct simplefb_format *format = NULL;
>  	int i;
> +	u32 reg;
>  
>  	pixel_format = crtc->primary->state->fb->pixel_format;
>  
> @@ -76,7 +77,11 @@ static int hdlcd_set_pxl_fmt(struct drm_crtc *crtc)
>  
>  	/* HDLCD uses 'bytes per pixel', zero means 1 byte */
>  	btpp = (format->bits_per_pixel + 7) / 8;
> -	hdlcd_write(hdlcd, HDLCD_REG_PIXEL_FORMAT, (btpp - 1) << 3);
> +	reg = (btpp - 1) << 3;
> +#ifdef __BIG_ENDIAN
> +	reg |= HDLCD_PIXEL_FMT_BIG_ENDIAN;
> +#endif
> +	hdlcd_write(hdlcd, HDLCD_REG_PIXEL_FORMAT, reg);
>  
>  	/*
>  	 * The format of the HDLCD_REG_<color>_SELECT register is:
> -- 
> 2.10.2.dirty
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯