| Message ID | 20170126162154.124287-1-djkurtz@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Jan 26, 2017 at 6:21 PM, Daniel Kurtz <djkurtz@chromium.org> wrote: > 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. Wouldn't be better to copy necessary stuff from parent device to its child? Like DMA mask propagation (I dunno if there are such in SPI, but at least many other drivers are doing that).
On 28/01/17 22:17, Andy Shevchenko wrote: > On Thu, Jan 26, 2017 at 6:21 PM, Daniel Kurtz <djkurtz@chromium.org> wrote: >> 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. > > Wouldn't be better to copy necessary stuff from parent device to its > child? Like DMA mask propagation (I dunno if there are such in SPI, > but at least many other drivers are doing that). Absolutely not. The "necessary stuff" includes arch-specific things which would require filling the SPI code with arch-specific #ifdefs, and may go as far as private data structures held by other drivers (e.g. IOMMUs) which the SPI code cannot even touch, let alone know what to do with. The "parent device" here *is* the real DMA master device (as described by firmware and configured by the arch code accordingly), so using any other device for DMA is just plain wrong. Robin.
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))
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@chromium.org> Fixes: c37f45b5f1cd ("spi: support spi without dma channel to use can_dma()") Cc: Leilk Liu <leilk.liu@mediatek.com> --- drivers/spi/spi.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)