Re: [PATCH 3/3] drm/i915/bios: be more explicit about discarding iomem address space

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, May 13, 2015 at 03:34:05PM +0300, Jani Nikula wrote:
> Add one explicit discard of __iomem address space qualifier in
> validate_vbt(), and respect it otherwise. This adds clarity in the code,
> and reduces the sparse warnings from the module to just one.
> 
> Quoting Daniel, "The vbt really is plain old memory. Except that it's
> reserved in the e820 table as something special and hence treated as io
> range by the kernel. But it is memory, hence casting away the __iomem is
> imo the right approach."
> 
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>

Merged entire series, thanks.
-Daniel

> ---
>  drivers/gpu/drm/i915/intel_bios.c | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_bios.c b/drivers/gpu/drm/i915/intel_bios.c
> index 6e018ba53035..198fc3c3291b 100644
> --- a/drivers/gpu/drm/i915/intel_bios.c
> +++ b/drivers/gpu/drm/i915/intel_bios.c
> @@ -1199,15 +1199,22 @@ static const struct dmi_system_id intel_no_opregion_vbt[] = {
>  	{ }
>  };
>  
> -static const struct bdb_header *validate_vbt(const void *base, size_t size,
> -					     const void *_vbt,
> +static const struct bdb_header *validate_vbt(const void __iomem *_base,
> +					     size_t size,
> +					     const void __iomem *_vbt,
>  					     const char *source)
>  {
> -	const struct vbt_header *vbt = _vbt;
> -	size_t offset;
> +	/*
> +	 * This is the one place where we explicitly discard the address space
> +	 * (__iomem) of the BIOS/VBT. (And this will cause a sparse complaint.)
> +	 * From now on everything is based on 'base', and treated as regular
> +	 * memory.
> +	 */
> +	const void *base = (const void *) _base;
> +	size_t offset = _vbt - _base;
> +	const struct vbt_header *vbt = base + offset;
>  	const struct bdb_header *bdb;
>  
> -	offset = _vbt - base;
>  	if (offset + sizeof(struct vbt_header) > size) {
>  		DRM_DEBUG_DRIVER("VBT header incomplete\n");
>  		return NULL;
> @@ -1235,14 +1242,14 @@ static const struct bdb_header *validate_vbt(const void *base, size_t size,
>  	return bdb;
>  }
>  
> -static const struct bdb_header *find_vbt(void *bios, size_t size)
> +static const struct bdb_header *find_vbt(void __iomem *bios, size_t size)
>  {
>  	const struct bdb_header *bdb = NULL;
>  	size_t i;
>  
>  	/* Scour memory looking for the VBT signature. */
>  	for (i = 0; i + 4 < size; i++) {
> -		if (memcmp(bios + i, "$VBT", 4) == 0) {
> +		if (ioread32(bios + i) == *((const u32 *) "$VBT")) {
>  			bdb = validate_vbt(bios, size, bios + i, "PCI ROM");
>  			break;
>  		}
> -- 
> 2.1.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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