linux-kernel - Re: [PATCH 4.19 182/267] spi: dw: Return any value retrieved from the dma

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Message-ID: <20200626151800.GA22242@maple.netwinder.org>
Date:   Fri, 26 Jun 2020 11:18:00 -0400
From:   Ralph Siemsen <ralph.siemsen@...aro.org>
To:     Serge Semin <Sergey.Semin@...kalelectronics.ru>
Cc:     Pavel Machek <pavel@...x.de>,
        Serge Semin <fancer.lancer@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Georgy Vlasov <Georgy.Vlasov@...kalelectronics.ru>,
        Ramil Zaripov <Ramil.Zaripov@...kalelectronics.ru>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Feng Tang <feng.tang@...el.com>,
        Rob Herring <robh+dt@...nel.org>, linux-mips@...r.kernel.org,
        devicetree@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 182/267] spi: dw: Return any value retrieved from
 the dma_transfer callback

Hi Serge, Pavel, Greg,

On Mon, Jun 22, 2020 at 11:51:21PM +0300, Serge Semin wrote:
>Hello Pavel
>
>On Fri, Jun 19, 2020 at 11:07:19PM +0200, Pavel Machek wrote:
>
>> Mainline patch simply changes return value, but code is different in
>> v4.19, and poll_transfer will now be avoided when dws->dma_mapped. Is
>> that a problem?
>
>Actually no.) In that old 4.19 context it's even better to return straight away
>no matter what value is returned by the dma_transfer() callback.

This patch changes the return dma_transfer return value from 0 to 1, 
however it was only done in spi-dw-mid.c func mid_spi_dma_transfer().

There is an identical function in spi-dw-mmio.c that needs the same 
treatment, otherwise access to the SPI device becomes erratic and even 
causes kernel to hang. Guess how I found this ;-)

So the following patch is needed as well, at least in 4.9 and 4.19, I 
did not check/test other versions. Mainline does not need this, since 
the code seems to have been refactored to avoid the duplication.

Regards,
-Ralph

diff --git a/drivers/spi/spi-dw-mmio.c b/drivers/spi/spi-dw-mmio.c
index c563c2815093..99641c485288 100644
--- a/drivers/spi/spi-dw-mmio.c
+++ b/drivers/spi/spi-dw-mmio.c
@@ -358,7 +358,7 @@ static int mmio_spi_dma_transfer(struct dw_spi *dws, struct spi_transfer *xfer)
 		dma_async_issue_pending(dws->txchan);
 	}
 
-	return 0;
+	return 1;
 }
 
 static void mmio_spi_dma_stop(struct dw_spi *dws)
-- 
2.17.1