linux-kernel - Re: [PATCH 4.19 15/28] spi: dw: use "smp_mb()" to avoid sending spi data error

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Message-ID: <20200607200910.GA13138@amd>
Date:   Sun, 7 Jun 2020 22:09:11 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        fengsheng <fengsheng5@...wei.com>,
        Xinwei Kong <kong.kongxinwei@...ilicon.com>,
        Mark Brown <broonie@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 15/28] spi: dw: use "smp_mb()" to avoid sending spi
 data error

Hi!

> 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 this patch add
> memory barrier to enable dw->rx and dw->rx_end to be visible and
> solve to send SPI data error.

So, this is apparently CPU-vs-device issue...

> +++ b/drivers/spi/spi-dw.c
> @@ -304,6 +304,9 @@ static int dw_spi_transfer_one(struct spi_controller *master,
>  	dws->len = transfer->len;
>  	spin_unlock_irqrestore(&dws->buf_lock, flags);
>  
> +	/* Ensure dw->rx and dw->rx_end are visible */
> +	smp_mb();
> +

But we use SMP-only memory barrier, thus the bug will still be there
in single-processor configurations. Should this be mb()?

Best regards,
								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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