Re: [PATCH 3/5] drm/i915/bios: Extract intel_spi_read16()

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 10 Sep 2024, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> The SPI VBT codepath only knows how to read 4 bytes at a time.
> So to read the 2 byte vbt_size it masks out the unwanted msbs.
> Hide that little implementation detail inside a new intel_spi_read16()
> helper. Alse rename the existing intel_spi_read() to intel_spi_read32()
> to make it clear what it does.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_bios.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_bios.c b/drivers/gpu/drm/i915/display/intel_bios.c
> index cc4a4cc2bf3e..cbbda94c3dab 100644
> --- a/drivers/gpu/drm/i915/display/intel_bios.c
> +++ b/drivers/gpu/drm/i915/display/intel_bios.c
> @@ -3053,13 +3053,18 @@ static struct vbt_header *firmware_get_vbt(struct intel_display *display,
>  	return vbt;
>  }
>  
> -static u32 intel_spi_read(struct intel_uncore *uncore, u32 offset)
> +static u32 intel_spi_read32(struct intel_uncore *uncore, u32 offset)
>  {
>  	intel_uncore_write(uncore, PRIMARY_SPI_ADDRESS, offset);
>  
>  	return intel_uncore_read(uncore, PRIMARY_SPI_TRIGGER);
>  }
>  
> +static u16 intel_spi_read16(struct intel_uncore *uncore, u32 offset)
> +{
> +	return intel_spi_read32(uncore, offset) & 0xffff;
> +}
> +
>  static struct vbt_header *spi_oprom_get_vbt(struct intel_display *display,
>  					    size_t *size)
>  {
> @@ -3078,7 +3083,7 @@ static struct vbt_header *spi_oprom_get_vbt(struct intel_display *display,
>  	oprom_offset &= OROM_OFFSET_MASK;
>  
>  	for (count = 0; count < oprom_size; count += 4) {
> -		data = intel_spi_read(&i915->uncore, oprom_offset + count);
> +		data = intel_spi_read32(&i915->uncore, oprom_offset + count);
>  		if (data == *((const u32 *)"$VBT")) {
>  			found = oprom_offset + count;
>  			break;
> @@ -3094,9 +3099,8 @@ static struct vbt_header *spi_oprom_get_vbt(struct intel_display *display,
>  	}
>  
>  	/* Get VBT size and allocate space for the VBT */
> -	vbt_size = intel_spi_read(&i915->uncore,
> -				  found + offsetof(struct vbt_header, vbt_size));
> -	vbt_size &= 0xffff;
> +	vbt_size = intel_spi_read16(&i915->uncore,
> +				    found + offsetof(struct vbt_header, vbt_size));

Pedantically if vbt_size was the last member of struct vbt_header this
could read past the checked size, but it's not and meh. Also nothing to
do with this change, apart from this hiding the detail. Still meh.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>


>  
>  	if (vbt_size > oprom_size - count) {
>  		drm_dbg(display->drm,
> @@ -3109,7 +3113,7 @@ static struct vbt_header *spi_oprom_get_vbt(struct intel_display *display,
>  		goto err_not_found;
>  
>  	for (count = 0; count < vbt_size; count += 4)
> -		*(vbt + store++) = intel_spi_read(&i915->uncore, found + count);
> +		*(vbt + store++) = intel_spi_read32(&i915->uncore, found + count);
>  
>  	if (!intel_bios_is_valid_vbt(display, vbt, vbt_size))
>  		goto err_free_vbt;

-- 
Jani Nikula, Intel