[PATCH 1/4] drm/radeon/dp: handle zero sized i2c over aux transactions

[Jani Nikula]

On Fri, 04 Apr 2014, Alex Deucher <alexdeucher at gmail.com> wrote:
> Needed for proper i2c over aux handling for certain
> monitors and configurations (e.g., dp bridges or
> adapters).
>
> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
> ---
>  drivers/gpu/drm/radeon/atombios_dp.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/radeon/atombios_dp.c b/drivers/gpu/drm/radeon/atombios_dp.c
> index 8b0ab17..e914008 100644
> --- a/drivers/gpu/drm/radeon/atombios_dp.c
> +++ b/drivers/gpu/drm/radeon/atombios_dp.c
> @@ -143,6 +143,7 @@ static int radeon_process_aux_ch(struct radeon_i2c_chan *chan,
>  }
>  
>  #define HEADER_SIZE 4
> +#define BARE_ADDRESS_SIZE 3
>  
>  static ssize_t
>  radeon_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
> @@ -160,13 +161,16 @@ radeon_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>  	tx_buf[0] = msg->address & 0xff;
>  	tx_buf[1] = msg->address >> 8;
>  	tx_buf[2] = msg->request << 4;
> -	tx_buf[3] = msg->size - 1;
> +	tx_buf[3] = msg->size ? (msg->size - 1) : 0;
>  
>  	switch (msg->request & ~DP_AUX_I2C_MOT) {
>  	case DP_AUX_NATIVE_WRITE:
>  	case DP_AUX_I2C_WRITE:
>  		tx_size = HEADER_SIZE + msg->size;
> -		tx_buf[3] |= tx_size << 4;
> +		if (msg->size == 0)
> +			tx_buf[3] |= BARE_ADDRESS_SIZE << 4;
> +		else
> +			tx_buf[3] |= tx_size << 4;
>  		memcpy(tx_buf + HEADER_SIZE, msg->buffer, msg->size);
>  		ret = radeon_process_aux_ch(chan,
>  					    tx_buf, tx_size, NULL, 0, delay, &ack);

I think your tz_size and tx_buf[3] are confused. Shouldn't you only send
3 bytes of tx_buf when msg->size == 0?

Disclaimer, I don't know anything about your hw and all that... :)

BR,
Jani.


> @@ -177,7 +181,10 @@ radeon_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>  	case DP_AUX_NATIVE_READ:
>  	case DP_AUX_I2C_READ:
>  		tx_size = HEADER_SIZE;
> -		tx_buf[3] |= tx_size << 4;
> +		if (msg->size == 0)
> +			tx_buf[3] |= BARE_ADDRESS_SIZE << 4;
> +		else
> +			tx_buf[3] |= tx_size << 4;
>  		ret = radeon_process_aux_ch(chan,
>  					    tx_buf, tx_size, msg->buffer, msg->size, delay, &ack);
>  		break;
> @@ -186,7 +193,7 @@ radeon_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
>  		break;
>  	}
>  
> -	if (ret > 0)
> +	if (ret >= 0)
>  		msg->reply = ack >> 4;
>  
>  	return ret;
> -- 
> 1.8.3.1
>

-- 
Jani Nikula, Intel Open Source Technology Center