[PATCH v7 05/11] dmaengine: Introduce DMA-device device_caps callback

Serge Semin
2020-07-09T22:47:07Z

There are DMA devices (like ours version of Synopsys DW DMAC) which have
DMA capabilities non-uniformly redistributed between the device channels.
In order to provide a way of exposing the channel-specific parameters to
the DMA engine consumers, we introduce a new DMA-device callback. In case
if provided it gets called from the dma_get_slave_caps() method and is
able to override the generic DMA-device capabilities.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: devicetree@vger.kernel.org

---

Changelog v3:
- This is a new patch created as a result of the discussion with Vinod and
Andy in the framework of DW DMA burst and LLP capabilities.

Changelog v5:
- Add in-line comment at the point of the device_caps callback invocation.
- Add doc-comment for the device_caps member of struct dma_device.
---
drivers/dma/dmaengine.c | 10 ++++++++++
include/linux/dmaengine.h | 4 ++++
2 files changed, 14 insertions(+)

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index ad56ad58932c..ed1fd376f1a5 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -599,6 +599,16 @@ int dma_get_slave_caps(struct dma_chan *chan, struct dma_slave_caps *caps)
caps->cmd_resume = !!device->device_resume;
caps->cmd_terminate = !!device->device_terminate_all;

+ /*
+ * DMA engine device might be configured with non-uniformly
+ * distributed slave capabilities per device channels. In this
+ * case the corresponding driver may provide the device_caps
+ * callback to override the generic capabilities with
+ * channel-specific ones.
+ */
+ if (device->device_caps)
+ device->device_caps(chan, caps);
+
return 0;
}
EXPORT_SYMBOL_GPL(dma_get_slave_caps);
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index a7e4d8dfdd19..298b721c8b9f 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -799,6 +799,8 @@ struct dma_filter {
* be called after period_len bytes have been transferred.
* @device_prep_interleaved_dma: Transfer expression in a generic way.
* @device_prep_dma_imm_data: DMA's 8 byte immediate data to the dst address
+ * @device_caps: May be used to override the generic DMA slave capabilities
+ * with per-channel specific ones
* @device_config: Pushes a new configuration to a channel, return 0 or an error
* code
* @device_pause: Pauses any transfer happening on a channel. Returns
@@ -899,6 +901,8 @@ struct dma_device {
struct dma_chan *chan, dma_addr_t dst, u64 data,
unsigned long flags);

+ void (*device_caps)(struct dma_chan *chan,
+ struct dma_slave_caps *caps);
int (*device_config)(struct dma_chan *chan,
struct dma_slave_config *config);
int (*device_pause)(struct dma_chan *chan);
--
2.26.2