[PATCH] video: Fix broken bcm2835 fb driver

[Roland Hieber]

On Tue, Sep 07, 2021 at 09:29:15AM +0200, Daniel Brát wrote:
> The bcm2835 framebuffer driver was broken, because the address of video
> buffer allocated for us by the GPU and returned through mailbox was
> used without converting it back to ARM address space. That unconverted
> address was also in the range of peripheral addresses, which caused
> other issues later on due to it being filled with garbage data.
> The offset by which to convert the address back can vary by device,
> so the value is read from devicetree 'dma-ranges' for somewhat portable
> operation.
> This fix was tested on Raspberry PI B+ and Raspberry PI 3B+.
> 
> Signed-off-by: Daniel Brát <danek.brat at gmail.com>
> ---
>  drivers/video/bcm2835.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/video/bcm2835.c b/drivers/video/bcm2835.c
> index d808bc5c9..2ebe912d0 100644
> --- a/drivers/video/bcm2835.c
> +++ b/drivers/video/bcm2835.c
> @@ -14,6 +14,7 @@
>  #include <malloc.h>
>  #include <xfuncs.h>
>  
> +#include <of_address.h>
>  #include <mach/mbox.h>
>  
>  struct bcm2835fb_info {
> @@ -58,9 +59,24 @@ static int bcm2835fb_probe(struct device_d *dev)
>  	BCM2835_MBOX_STACK_ALIGN(struct msg_fb_query, msg_query);
>  	BCM2835_MBOX_STACK_ALIGN(struct msg_fb_setup, msg_setup);
>  	struct bcm2835fb_info *info;
> +	struct device_node *soc;
>  	u32 w, h;
> +	u64 dma_addr, cpu_addr, _region_size;
> +	phys_addr_t buffer_addr;
>  	int ret;
>  
> +	soc = of_find_node_by_path("/soc");
> +	if (!soc) {
> +		dev_err(dev, "could not find required of node /soc\n");

Nit: I'd use "OF" in capitals to ease human parsing and prevent
confusing with the English preposition.

> +		return -ENODEV;
> +	}
> +
> +	ret = of_dma_get_range(soc, &dma_addr, &cpu_addr, &_region_size);
> +	if (ret) {
> +		dev_err(dev, "of node /soc has no dma-ranges\n");

Here too.

 - Roland

> +		return ret;
> +	}
> +
>  	BCM2835_MBOX_INIT_HDR(msg_query);
>  	BCM2835_MBOX_INIT_TAG_NO_REQ(&msg_query->physical_w_h,
>  					GET_PHYSICAL_W_H);
> @@ -99,10 +115,11 @@ static int bcm2835fb_probe(struct device_d *dev)
>  		return ret;
>  	}
>  
> +	buffer_addr = (msg_setup->allocate_buffer.body.resp.fb_address & ~dma_addr) + cpu_addr;
> +
>  	info = xzalloc(sizeof *info);
>  	info->fbi.fbops = &bcm2835fb_ops;
> -	info->fbi.screen_base =
> -	   (void *)msg_setup->allocate_buffer.body.resp.fb_address;
> +	info->fbi.screen_base = phys_to_virt(buffer_addr);
>  	info->fbi.xres = msg_setup->physical_w_h.body.resp.width;
>  	info->fbi.yres = msg_setup->physical_w_h.body.resp.height;
>  	info->fbi.bits_per_pixel = 16;
> -- 
> 2.17.1
> 
> 
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Roland Hieber, Pengutronix e.K.          | r.hieber at pengutronix.de     |
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