Re: [PATCH] spi: dw: use "smp_mb()" to avoid sending spi data error

[Mark Brown <broonie@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 911 bytes --]

On Thu, Dec 26, 2019 at 05:21:28PM +0800, Xinwei Kong wrote:
> this patch will add memory barrier to ensure this "struct dw_spi *dws"
> to complete data setting before enabling this SPI hardware interrupt.
> eg:
> it will fix to this following low possibility error in testing environment
> which using SPI control to connect TPM Modules

> --- a/drivers/spi/spi-dw.c
> +++ b/drivers/spi/spi-dw.c
> @@ -288,6 +288,8 @@ static int dw_spi_transfer_one(struct spi_controller *master,
>  	dws->rx_end = dws->rx + transfer->len;
>  	dws->len = transfer->len;
>  
> +	smp_mb();
> +
>  	spi_enable_chip(dws, 0);

I'd be much more comfortable here if I understood what this was
supposed to be syncing - what exactly gets flushed here and why
is a memory barrier enough to ensure it's synced?  A comment in
the code would be especially good so anyone modifying the code
understands this in future.

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]