linux-kernel - Re: [PATCH 03/10] drm/sun4i: Remove obsolete references to PHYS

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Date:   Mon, 11 Apr 2022 17:37:49 +0200
From:   Jernej Škrabec <jernej.skrabec@...il.com>
To:     Chen-Yu Tsai <wens@...e.org>, Maxime Ripard <mripard@...nel.org>,
        Samuel Holland <samuel@...lland.org>
Cc:     Samuel Holland <samuel@...lland.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH 03/10] drm/sun4i: Remove obsolete references to PHYS_OFFSET

Dne ponedeljek, 11. april 2022 ob 06:34:15 CEST je Samuel Holland napisal(a):
> commit b4bdc4fbf8d0 ("soc: sunxi: Deal with the MBUS DMA offsets in a
> central place") added a platform device notifier that sets the DMA
> offset for all of the display engine frontend and backend devices.
> 
> The code applying the offset to DMA buffer physical addresses was then
> removed from the backend driver in commit 756668ba682e ("drm/sun4i:
> backend: Remove the MBUS quirks"), but the code subtracting PHYS_OFFSET
> was left in the frontend driver.
> 
> As a result, the offset was applied twice in the frontend driver. This
> likely went unnoticed because it only affects specific configurations
> (scaling or certain pixel formats) where the frontend is used, on boards
> with both one of these older SoCs and more than 1 GB of DRAM.
> 
> In addition, the references to PHYS_OFFSET prevent compiling the driver
> on architectures where PHYS_OFFSET is not defined.
> 
> Fixes: b4bdc4fbf8d0 ("soc: sunxi: Deal with the MBUS DMA offsets in a central 
place")
> Signed-off-by: Samuel Holland <samuel@...lland.org>

Good catch! Actually, people complained about non-working display on 
Cubietruck IIRC, which has 2 GB of RAM.

Did you test this on HW?

Reviewed-by: Jernej Skrabec <jernej.skrabec@...il.com>

Best regards,
Jernej

> ---
> 
>  drivers/gpu/drm/sun4i/sun4i_frontend.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/sun4i/sun4i_frontend.c b/drivers/gpu/drm/sun4i/
sun4i_frontend.c
> index 56ae38389db0..462fae73eae9 100644
> --- a/drivers/gpu/drm/sun4i/sun4i_frontend.c
> +++ b/drivers/gpu/drm/sun4i/sun4i_frontend.c
> @@ -222,13 +222,11 @@ void sun4i_frontend_update_buffer(struct sun4i_frontend 
*frontend,
>  
>  	/* Set the physical address of the buffer in memory */
>  	paddr = drm_fb_cma_get_gem_addr(fb, state, 0);
> -	paddr -= PHYS_OFFSET;
>  	DRM_DEBUG_DRIVER("Setting buffer #0 address to %pad\n", &paddr);
>  	regmap_write(frontend->regs, SUN4I_FRONTEND_BUF_ADDR0_REG, paddr);
>  
>  	if (fb->format->num_planes > 1) {
>  		paddr = drm_fb_cma_get_gem_addr(fb, state, swap ? 2 : 
1);
> -		paddr -= PHYS_OFFSET;
>  		DRM_DEBUG_DRIVER("Setting buffer #1 address to %pad\n", 
&paddr);
>  		regmap_write(frontend->regs, 
SUN4I_FRONTEND_BUF_ADDR1_REG,
>  			     paddr);
> @@ -236,7 +234,6 @@ void sun4i_frontend_update_buffer(struct sun4i_frontend 
*frontend,
>  
>  	if (fb->format->num_planes > 2) {
>  		paddr = drm_fb_cma_get_gem_addr(fb, state, swap ? 1 : 
2);
> -		paddr -= PHYS_OFFSET;
>  		DRM_DEBUG_DRIVER("Setting buffer #2 address to %pad\n", 
&paddr);
>  		regmap_write(frontend->regs, 
SUN4I_FRONTEND_BUF_ADDR2_REG,
>  			     paddr);
> -- 
> 2.35.1
> 
>