2023-05-12 11:22:07

by Joy Chakraborty

Subject: [PATCH v11 3/3] spi: dw: Round of n_bytes to power of 2

n_bytes variable in the driver represents the number of bytes per word
that needs to be sent/copied to fifo. Bits/word can be between 8 and 32
bits from the client but in memory they are a power of 2, same is mentioned
in spi.h header:
"
* @bits_per_word: Data transfers involve one or more words; word sizes
* like eight or 12 bits are common. In-memory wordsizes are
* powers of two bytes (e.g. 20 bit samples use 32 bits).
* This may be changed by the device's driver, or left at the
* default (0) indicating protocol words are eight bit bytes.
* The spi_transfer.bits_per_word can override this for each transfer.
"

Hence, round of n_bytes to a power of 2 to avoid values like 3 which
would generate unalligned/odd accesses to memory/fifo.

Fixes: a51acc2400d4 ("spi: dw: Add support for 32-bits max xfer size")
Suggested-by: Andy Shevchenko <[email protected]>
Signed-off-by: Joy Chakraborty <[email protected]>
Reviewed-by: Serge Semin <[email protected]>
Tested-by: Serge Semin <[email protected]>
* tested on Baikal-T1 based system with DW SPI-looped back interface
transferring a chunk of data with DFS:8,12,16.
---
drivers/spi/spi-dw-core.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-dw-core.c b/drivers/spi/spi-dw-core.c
index ae3108c70f50..7778b19bcb6c 100644
--- a/drivers/spi/spi-dw-core.c
+++ b/drivers/spi/spi-dw-core.c
@@ -426,7 +426,10 @@ static int dw_spi_transfer_one(struct spi_controller *master,
int ret;

dws->dma_mapped = 0;
- dws->n_bytes = DIV_ROUND_UP(transfer->bits_per_word, BITS_PER_BYTE);
+ dws->n_bytes =
+ roundup_pow_of_two(DIV_ROUND_UP(transfer->bits_per_word,
+ BITS_PER_BYTE));
+
dws->tx = (void *)transfer->tx_buf;
dws->tx_len = transfer->len / dws->n_bytes;
dws->rx = transfer->rx_buf;
--
2.40.1.606.ga4b1b128d6-goog

2023-05-17 23:22:33

by Andy Shevchenko

Subject: Re: [PATCH v11 3/3] spi: dw: Round of n_bytes to power of 2

On Fri, May 12, 2023 at 10:47:45AM +0000, Joy Chakraborty wrote:
> n_bytes variable in the driver represents the number of bytes per word
> that needs to be sent/copied to fifo. Bits/word can be between 8 and 32

FIFO

> bits from the client but in memory they are a power of 2, same is mentioned
> in spi.h header:

> "

Just a blank line is enough here.

> * @bits_per_word: Data transfers involve one or more words; word sizes
> * like eight or 12 bits are common. In-memory wordsizes are
> * powers of two bytes (e.g. 20 bit samples use 32 bits).
> * This may be changed by the device's driver, or left at the
> * default (0) indicating protocol words are eight bit bytes.
> * The spi_transfer.bits_per_word can override this for each transfer.
> "

And here.

> Hence, round of n_bytes to a power of 2 to avoid values like 3 which
> would generate unalligned/odd accesses to memory/fifo.

FIFO

> Fixes: a51acc2400d4 ("spi: dw: Add support for 32-bits max xfer size")
> Suggested-by: Andy Shevchenko <[email protected]>
> Signed-off-by: Joy Chakraborty <[email protected]>
> Reviewed-by: Serge Semin <[email protected]>
> Tested-by: Serge Semin <[email protected]>

> * tested on Baikal-T1 based system with DW SPI-looped back interface
> transferring a chunk of data with DFS:8,12,16.

This shouldn't be here. It's not a tag.

--
With Best Regards,
Andy Shevchenko