Re: [PATCH] drm/bridge: analogix_dp: Don't return -EBUSY when msg->size is 0 in aux transaction

From: Zain Wang
Date: Sun Feb 19 2017 - 23:12:19 EST

Hi Tomasz,

å 2017/2/20 10:40, Tomasz Figa åé:
Hi Zain,

On Mon, Feb 13, 2017 at 6:27 PM, zain wang <wzz@xxxxxxxxxxxxxx> wrote:
The analogix_dp_transfer() will return -EBUSY if num_transferred is zero.
But sometimes we will send a bare address packet to start the transaction,
like drm_dp_i2c_xfer() show:
/* Send a bare address packet to start the transaction.
* Zero sized messages specify an address only (bare
* address) transaction.
msg.buffer = NULL;
msg.size = 0;
err = drm_dp_i2c_do_msg(aux, &msg);

In this case, the msg->size is zero, so the num_transferred will be zero too.
We can't return -EBUSY here, let's we return num_transferred if num_transferred
equals msg->size.

Please see my question inline.

Signed-off-by: zain wang <wzz@xxxxxxxxxxxxxx>
drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c b/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c
index 303083a..5384aca 100644
--- a/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c
+++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_reg.c
@@ -1162,5 +1162,5 @@ ssize_t analogix_dp_transfer(struct analogix_dp_device *dp,
(msg->request & ~DP_AUX_I2C_MOT) == DP_AUX_NATIVE_READ)

- return num_transferred > 0 ? num_transferred : -EBUSY;
+ return (num_transferred == msg->size) ? num_transferred : -EBUSY;
I might be missing something but, looking at the code, I don't see any
possibility of num_transferred ever being different than msg->size. To
be honest, it doesn't seem to even make any sense keeping the local
variable there, because msg->size can be simply always returned, as
errors are handled by jumping to aux_error label.
Yeah, I agree with you.
The better way to fix this issue is to revert the changes
(returning num_transferred directly may be better here)

Maybe we can revert the changes above with some new comment.
@Sean, How do you think about Tomasz's comment?


Best regards,