On Wed, Aug 07, 2019 at 06:48:07PM +0200, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
> The patch below does not apply to the 5.2-stable tree.
That's odd, it works for me:
$ git fetch linux-stable
$ git checkout linux-stable/linux-5.2.y
Checking out files: 100% (43562/43562), done.
HEAD is now at 5697a9d... Linux 5.2.7
$ git am /tmp/pt
Applying: spi: bcm2835: Fix 3-wire mode if DMA is enabled
Could you be a little more specific why it couldn't be applied
when you tried it?
Thanks,
Lukas
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.
>
> thanks,
>
> greg k-h
>
> ------------------ original commit in Linus's tree ------------------
>
> From 8d8bef50365847134b51c1ec46786bc2873e4e47 Mon Sep 17 00:00:00 2001
> From: Lukas Wunner <lukas@xxxxxxxxx>
> Date: Wed, 3 Jul 2019 12:29:31 +0200
> Subject: [PATCH] spi: bcm2835: Fix 3-wire mode if DMA is enabled
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
>
> Commit 6935224da248 ("spi: bcm2835: enable support of 3-wire mode")
> added 3-wire support to the BCM2835 SPI driver by setting the REN bit
> (Read Enable) in the CS register when receiving data. The REN bit puts
> the transmitter in high-impedance state. The driver recognizes that
> data is to be received by checking whether the rx_buf of a transfer is
> non-NULL.
>
> Commit 3ecd37edaa2a ("spi: bcm2835: enable dma modes for transfers
> meeting certain conditions") subsequently broke 3-wire support because
> it set the SPI_MASTER_MUST_RX flag which causes spi_map_msg() to replace
> rx_buf with a dummy buffer if it is NULL. As a result, rx_buf is
> *always* non-NULL if DMA is enabled.
>
> Reinstate 3-wire support by not only checking whether rx_buf is non-NULL,
> but also checking that it is not the dummy buffer.
>
> Fixes: 3ecd37edaa2a ("spi: bcm2835: enable dma modes for transfers meeting certain conditions")
> Reported-by: Nuno Sá <nuno.sa@xxxxxxxxxx>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v4.2+
> Cc: Martin Sperl <kernel@xxxxxxxxxxxxxxxx>
> Acked-by: Stefan Wahren <wahrenst@xxxxxxx>
> Link: https://lore.kernel.org/r/328318841455e505370ef8ecad97b646c033dc8a.1562148527.git.lukas@xxxxxxxxx
> Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
>
> diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
> index 6f243a90c844..840b1b8ff3dc 100644
> --- a/drivers/spi/spi-bcm2835.c
> +++ b/drivers/spi/spi-bcm2835.c
> @@ -834,7 +834,8 @@ static int bcm2835_spi_transfer_one(struct spi_controller *ctlr,
> bcm2835_wr(bs, BCM2835_SPI_CLK, cdiv);
>
> /* handle all the 3-wire mode */
> - if ((spi->mode & SPI_3WIRE) && (tfr->rx_buf))
> + if (spi->mode & SPI_3WIRE && tfr->rx_buf &&
> + tfr->rx_buf != ctlr->dummy_rx)
> cs |= BCM2835_SPI_CS_REN;
> else
> cs &= ~BCM2835_SPI_CS_REN;
>
