Re: [PATCH] spi: spi-imx: spi_imx_transfer_one(): check for DMA transfer first

From: Frieder Schrempf <frieder.schrempf@kontron.de>
To: Marc Kleine-Budde <mkl@pengutronix.de>,
	Mark Brown <broonie@kernel.org>,
	linux-spi@vger.kernel.org
Cc: kernel@pengutronix.de, Shawn Guo <shawnguo@kernel.org>,
	NXP Linux Team <linux-imx@nxp.com>,
	linux-arm-kernel@lists.infradead.org,
	Fabio Estevam <festevam@gmail.com>,
	David Jander <david@protonic.nl>,
	stable@vger.kernel.org
Subject: Re: [PATCH] spi: spi-imx: spi_imx_transfer_one(): check for DMA transfer first
Date: Wed, 16 Nov 2022 18:03:31 +0100	[thread overview]
Message-ID: <bfca8a49-a443-feb0-6fa8-0e7d17899a5b@kontron.de> (raw)
In-Reply-To: <20221116164930.855362-1-mkl@pengutronix.de>

On 16.11.22 17:49, Marc Kleine-Budde wrote:
> The SPI framework checks for each transfer (with the struct
> spi_controller::can_dma callback) whether the driver wants to use DMA
> for the transfer. If the driver returns true, the SPI framework will
> map the transfer's data to the device, start the actual transfer and
> map the data back.
> 
> In commit 07e759387788 ("spi: spi-imx: add PIO polling support") the
> spi-imx driver's spi_imx_transfer_one() function was extended. If the
> estimated duration of a transfer does not exceed a configurable
> duration, a polling transfer function is used. This check happens
> before checking if the driver decided earlier for a DMA transfer.
> 
> If spi_imx_can_dma() decided to use a DMA transfer, and the user
> configured a big maximum polling duration, a polling transfer will be
> used. The DMA unmap after the transfer destroys the transferred data.
> 
> To fix this problem check in spi_imx_transfer_one() if the driver
> decided for DMA transfer first, then check the limits for a polling
> transfer.
> 
> Fixes: 07e759387788 ("spi: spi-imx: add PIO polling support")
> Link: https://lore.kernel.org/all/20221111003032.82371-1-festevam@gmail.com
> Reported-by: Frieder Schrempf <frieder.schrempf@kontron.de>
> Reported-by: Fabio Estevam <festevam@gmail.com>
> Tested-by: Fabio Estevam <festevam@gmail.com>
> Cc: David Jander <david@protonic.nl>
> Cc: stable@vger.kernel.org
> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>