On Tue, Nov 16, 2021 at 06:14:23AM +0000, Tudor.Ambarus@microchip.com wrote:

On 11/15/21 5:58 PM, Greg KH wrote:

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On Mon, Nov 15, 2021 at 04:30:04PM +0200, Tudor Ambarus wrote:

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dma_cookie_t < 0 indicates an error code, check for it.

Very odd changelog text, please be more descriptive about what is
happening here.

The tx_submit() method of struct dma_async_tx_descriptor is entitled to do
sanity checks and return errors if encountered. It's not the case for the
DMA controller drivers that this client is using (at_h/xdmac), because they
currently don't do sanity checks and always return a positive cookie at
tx_submit() method. In case the controller drivers will implement sanity
checks and return errors, print a message so that the client will be informed
that something went wrong at tx_submit() level.

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Signed-off-by: Tudor Ambarus <redacted>
---
 drivers/tty/serial/atmel_serial.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 2c99a47a2535..376f7a9c2868 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c

@@ -1004,6 +1004,11 @@ static void atmel_tx_dma(struct uart_port *port)
              desc->callback = atmel_complete_tx_dma;
              desc->callback_param = atmel_port;
              atmel_port->cookie_tx = dmaengine_submit(desc);
+             if (dma_submit_error(atmel_port->cookie_tx)) {
+                     dev_err(port->dev, "dma_submit_error %d\n",
+                             atmel_port->cookie_tx);
+                     return;

What can a user do with this error message?

will be informed that something went wrong at tx_submit() level.

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Have you seen this happen in real life?

No. I debugged a locking problem and I observed that dma_submit_error() is not called,
so I thought to update this.

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What commit does this "fix"?

This is rather an improvement, but if you're looking for a fixes tag, I think
we can use:
Fixes: 08f738be88bb ("serial: at91: add tx dma support")

I'll send a v2 as part of a bigger series. If you find this patch does not worth it,
I can as well drop it.

Please resend it because as-is, I can not take it.

thanks,

greg k-h