[PATCH] drm/radeon: fix atom aux payload size check for writes

[Michel Dänzer]

On 21.02.2015 01:56, Alex Deucher wrote:
> The atom aux param interface only supports 4 bits for
> the total write transfer size (header + payload).  This
> limits us to 12 bytes of payload rather than 16.  Add a
> check for this. Reads are not affected.
> 
> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
> ---
>  drivers/gpu/drm/radeon/atombios_dp.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/radeon/atombios_dp.c b/drivers/gpu/drm/radeon/atombios_dp.c
> index 5bf825d..c57706e6 100644
> --- a/drivers/gpu/drm/radeon/atombios_dp.c
> +++ b/drivers/gpu/drm/radeon/atombios_dp.c
> @@ -178,6 +178,13 @@ radeon_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>  	switch (msg->request & ~DP_AUX_I2C_MOT) {
>  	case DP_AUX_NATIVE_WRITE:
>  	case DP_AUX_I2C_WRITE:
> +		/* The atom implementation only supports writes with a max payload of
> +		 * 12 bytes since it uses 4 bits for the total count (header + payload)
> +		 * in the parameter space.  The atom interface supports 16 byte
> +		 * payloads for reads. The hw itself supports up to 16 bytes of payload.
> +		 */
> +		if (WARN_ON(msg->size > 12))
> +			return -E2BIG;
>  		/* tx_size needs to be 4 even for bare address packets since the atom
>  		 * table needs the info in tx_buf[3].
>  		 */
> 

Might be safer to use WARN_ON_ONCE to avoid spamming dmesg if the
warning ever gets triggered.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer