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

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Message-ID: <20200103010409.GG3897@sirena.org.uk>
Date:   Fri, 3 Jan 2020 01:04:09 +0000
From:   Mark Brown <broonie@...nel.org>
To:     kongxinwei <kong.kongxinwei@...ilicon.com>
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, fengsheng <fengsheng5@...wei.com>
Subject: Re: [PATCH] spi: dw: use "smp_mb()" to avoid sending spi data error

On Sat, Dec 28, 2019 at 04:31:53PM +0800, kongxinwei wrote:

> > 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.

> Because of out-of-order execution about some CPU architecture,
> In this debug stage we find Completing spi interrupt enable ->
> prodrucing TXEI interrupt -> running "interrupt_transfer" function
> will prior to set "dw->rx and dws->rx_end" data, so it will result
> in SPI sending error

Could you update the commit message to say that, and ideally also
add a comment saying something like "Ensure dw->rx and dw->rx_end
are visible" please?

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