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

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Message-ID: <20200619210719.GB12233@amd>
Date:   Fri, 19 Jun 2020 23:07:19 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        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

On Fri 2020-06-19 16:32:47, Greg Kroah-Hartman wrote:
> From: Serge Semin <Sergey.Semin@...kalelectronics.ru>
> 
> [ Upstream commit f0410bbf7d0fb80149e3b17d11d31f5b5197873e ]
> 
> DW APB SSI DMA-part of the driver may need to perform the requested
> SPI-transfer synchronously. In that case the dma_transfer() callback
> will return 0 as a marker of the SPI transfer being finished so the
> SPI core doesn't need to wait and may proceed with the SPI message
> trasnfers pumping procedure. This will be needed to fix the problem
> when DMA transactions are finished, but there is still data left in
> the SPI Tx/Rx FIFOs being sent/received. But for now make dma_transfer
> to return 1 as the normal dw_spi_transfer_one() method.

As far as I understand, this is support for new SoC, not a fix?

> +++ b/drivers/spi/spi-dw.c
> @@ -383,11 +383,8 @@ static int dw_spi_transfer_one(struct spi_controller *master,
>  
>  	spi_enable_chip(dws, 1);
>  
> -	if (dws->dma_mapped) {
> -		ret = dws->dma_ops->dma_transfer(dws, transfer);
> -		if (ret < 0)
> -			return ret;
> -	}
> +	if (dws->dma_mapped)
> +		return dws->dma_ops->dma_transfer(dws, transfer);
>  
>  	if (chip->poll_mode)
>  		return poll_transfer(dws);

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?

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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