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spi: atmel: Prevent false timeouts on long transfers 

A slow SPI bus clocks at ~20MHz, which means it would transfer about
2500 bytes per second with a single data line. Big transfers, like when
dealing with flashes can easily reach a few MiB. The current DMA timeout
is set to 1 second, which means any working transfer of about 4MiB will
always be cancelled.

With the above derivations, on a slow bus, we can assume every byte will
take at most 0.4ms. Said otherwise, we could add 4ms to the 1-second
timeout delay every 10kiB. On a 4MiB transfer, it would bring the
timeout delay up to 2.6s which still seems rather acceptable for a
timeout.

The consequence of this is that long transfers might be allowed, which
hence requires the need to interrupt the transfer if wanted by the
user. We can hence switch to the _interruptible variant of
wait_for_completion. This leads to a little bit more handling to also
handle the interrupted case but looks really acceptable overall.

While at it, we drop the useless, noisy and redundant WARN_ON() call.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Ryan Wanner <ryan.wanner@microchip.com>
Link: https://lore.kernel.org/r/Message-Id: <20230622090634.3411468-3-miquel.raynal@bootlin.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Miquel Raynal 2023-06-22 11:06:33 +02:00 committed by Mark Brown
parent d8e4ebf870
commit e0205d6203
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GPG Key ID: 24D68B725D5487D0
1 changed files with 11 additions and 7 deletions
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18
drivers/spi/spi-atmel.c
View File

@ -233,7 +233,8 @@
*/
#define DMA_MIN_BYTES 16
#define SPI_DMA_TIMEOUT (msecs_to_jiffies(1000))
#define SPI_DMA_MIN_TIMEOUT (msecs_to_jiffies(1000))
#define SPI_DMA_TIMEOUT_PER_10K (msecs_to_jiffies(4))
#define AUTOSUSPEND_TIMEOUT 2000
@ -1279,7 +1280,8 @@ static int atmel_spi_one_transfer(struct spi_controller *host,
struct atmel_spi_device *asd;
int timeout;
int ret;
unsigned long dma_timeout;
unsigned int dma_timeout;
long ret_timeout;
as = spi_controller_get_devdata(host);
@ -1333,11 +1335,13 @@ static int atmel_spi_one_transfer(struct spi_controller *host,
atmel_spi_unlock(as);
}
dma_timeout = wait_for_completion_timeout(&as->xfer_completion,
SPI_DMA_TIMEOUT);
if (WARN_ON(dma_timeout == 0)) {
dev_err(&spi->dev, "spi transfer timeout\n");
as->done_status = -EIO;
dma_timeout = msecs_to_jiffies(spi_controller_xfer_timeout(host, xfer));
ret_timeout = wait_for_completion_interruptible_timeout(&as->xfer_completion,
dma_timeout);
if (ret_timeout <= 0) {
dev_err(&spi->dev, "spi transfer %s\n",
!ret_timeout ? "timeout" : "canceled");
as->done_status = ret_timeout < 0 ? ret_timeout : -EIO;
}
if (as->done_status)