linux-kernel - [PATCH 1/2] spi: When no dma_chan map buffers with spi

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Message-Id: <20170126162154.124287-1-djkurtz@chromium.org>
Date:   Fri, 27 Jan 2017 00:21:53 +0800
From:   Daniel Kurtz <djkurtz@...omium.org>
To:     unlisted-recipients:; (no To-header on input)
Cc:     dtor@...omium.org, groeck@...omium.org, drinkcat@...omium.org,
        Robin Murphy <robin.murphy@....com>,
        Daniel Kurtz <djkurtz@...omium.org>,
        Leilk Liu <leilk.liu@...iatek.com>,
        Mark Brown <broonie@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-spi@...r.kernel.org (open list:SPI SUBSYSTEM),
        linux-kernel@...r.kernel.org (open list),
        linux-arm-kernel@...ts.infradead.org (moderated list:ARM/Mediatek SoC
        support),
        linux-mediatek@...ts.infradead.org (moderated list:ARM/Mediatek SoC
        support)
Subject: [PATCH 1/2] spi: When no dma_chan map buffers with spi_master's parent 

Back before commit 1dccb598df54 ("arm64: simplify dma_get_ops"), for
arm64, devices for which dma_ops were not explicitly set were automatically
configured to use swiotlb_dma_ops, since this was hard-coded as the
global "dma_ops" in arm64_dma_init().

Now that global "dma_ops" has been removed, all devices much have their
dma_ops explicitly set by a call to arch_setup_dma_ops(), otherwise the
device is assigned dummy_dma_ops, and thus calls to map_sg for such a
device will fail (return 0).

Mediatek SPI uses DMA but does not use a dma channel.  Support for this
was added by commit c37f45b5f1cd ("spi: support spi without dma channel
to use can_dma()"), which uses the master_spi dev to DMA map buffers.

The master_spi device is not a platform device, rather it is created
in spi_alloc_device(), and therefore its dma_ops are never set.

Therefore, when the mediatek SPI driver when it does DMA (for large SPI
transactions > 32 bytes), SPI will use spi_map_buf()->dma_map_sg() to
map the buffer for use in DMA.  But dma_map_sg()->dma_map_sg_attrs() returns
0, because ops->map_sg is dummy_dma_ops->__dummy_map_sg, and hence
spi_map_buf() returns -ENOMEM (-12).

Fix this by using the real spi_master's parent device which should be a
real physical device with DMA properties.

Signed-off-by: Daniel Kurtz <djkurtz@...omium.org>
Fixes: c37f45b5f1cd ("spi: support spi without dma channel to use can_dma()")
Cc: Leilk Liu <leilk.liu@...iatek.com>
---
 drivers/spi/spi.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 656dd3e3220c..f4d412e48e1c 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -805,12 +805,12 @@ static int __spi_map_msg(struct spi_master *master, struct spi_message *msg)
 	if (master->dma_tx)
 		tx_dev = master->dma_tx->device->dev;
 	else
-		tx_dev = &master->dev;
+		tx_dev = master->dev.parent;

 	if (master->dma_rx)
 		rx_dev = master->dma_rx->device->dev;
 	else
-		rx_dev = &master->dev;
+		rx_dev = master->dev.parent;

 	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
 		if (!master->can_dma(master, msg->spi, xfer))
@@ -852,12 +852,12 @@ static int __spi_unmap_msg(struct spi_master *master, struct spi_message *msg)
 	if (master->dma_tx)
 		tx_dev = master->dma_tx->device->dev;
 	else
-		tx_dev = &master->dev;
+		tx_dev = master->dev.parent;

 	if (master->dma_rx)
 		rx_dev = master->dma_rx->device->dev;
 	else
-		rx_dev = &master->dev;
+		rx_dev = master->dev.parent;

 	list_for_each_entry(xfer, &msg->transfers, transfer_list) {
 		if (!master->can_dma(master, msg->spi, xfer))
-- 
2.11.0.483.g087da7b7c-goog