linux-kernel - Re: [PATCH v11 3/3] spi: dw: Round of n

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Message-ID: <ZGVdK9jQ+zxRvOze@smile.fi.intel.com>
Date:   Thu, 18 May 2023 02:03:07 +0300
From:   Andy Shevchenko <andriy.shevchenko@...el.com>
To:     Joy Chakraborty <joychakr@...gle.com>
Cc:     Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
        linux-kernel@...r.kernel.org, manugautam@...gle.com,
        Serge Semin <fancer.lancer@...il.com>
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 <andriy.shevchenko@...el.com>
> Signed-off-by: Joy Chakraborty <joychakr@...gle.com>
> Reviewed-by: Serge Semin <fancer.lancer@...il.com>
> Tested-by: Serge Semin <fancer.lancer@...il.com>

> * 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