On Fri, Jun 29, 2018 at 9:37 AM, Vinod [off-list ref] wrote:

On 25-06-18, 11:27, Andrea Merello wrote:

quoted

The AXIDMA and CDMA HW can be either direct-access or scatter-gather
version. These are SW incompatible.

The driver can handle both version: a DT property was used to

                                ^^^^
versions

OK

quoted

tell the driver whether to assume the HW is is scatter-gather mode.

                                           ^^^^^
is in?

Yes, it is. Thanks

quoted

This patch makes the driver to autodetect this information. The DT
property is not required anymore.

No changes for VDMA.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: devicetree@vger.kernel.org
Cc: Radhey Shyam Pandey <redacted>
Signed-off-by: Andrea Merello <redacted>
Reviewed-by: Radhey Shyam Pandey <redacted>
---
Changes in v2:
      - autodetect only in !VDMA case
Changes in v3:
      - cc DT maintainers/ML
---
 drivers/dma/xilinx/xilinx_dma.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index 7f0ab904b749..43fcc71ff287 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c

@@ -86,6 +86,7 @@
 #define XILINX_DMA_DMASR_DMA_DEC_ERR         BIT(6)
 #define XILINX_DMA_DMASR_DMA_SLAVE_ERR               BIT(5)
 #define XILINX_DMA_DMASR_DMA_INT_ERR         BIT(4)
+#define XILINX_DMA_DMASR_SG_MASK             BIT(3)
 #define XILINX_DMA_DMASR_IDLE                        BIT(1)
 #define XILINX_DMA_DMASR_HALTED              BIT(0)
 #define XILINX_DMA_DMASR_DELAY_MASK          GENMASK(31, 24)

@@ -406,7 +407,6 @@ struct xilinx_dma_config {
  * @dev: Device Structure
  * @common: DMA device structure
  * @chan: Driver specific DMA channel
- * @has_sg: Specifies whether Scatter-Gather is present or not
  * @mcdma: Specifies whether Multi-Channel is present or not
  * @flush_on_fsync: Flush on frame sync
  * @ext_addr: Indicates 64 bit addressing is supported by dma device

@@ -426,7 +426,6 @@ struct xilinx_dma_device {
      struct device *dev;
      struct dma_device common;
      struct xilinx_dma_chan *chan[XILINX_DMA_MAX_CHANS_PER_DEVICE];
-     bool has_sg;
      bool mcdma;
      u32 flush_on_fsync;
      bool ext_addr;

@@ -2393,7 +2392,6 @@ static int xilinx_dma_chan_probe(struct xilinx_dma_device *xdev,

      chan->dev = xdev->dev;
      chan->xdev = xdev;
-     chan->has_sg = xdev->has_sg;
      chan->desc_pendingcount = 0x0;
      chan->ext_addr = xdev->ext_addr;
      /* This variable ensures that descriptors are not

@@ -2486,6 +2484,15 @@ static int xilinx_dma_chan_probe(struct xilinx_dma_device *xdev,
              chan->stop_transfer = xilinx_dma_stop_transfer;
      }

+     /* check if SG is enabled (only for AXIDMA and CDMA) */
+     if (xdev->dma_config->dmatype != XDMA_TYPE_VDMA) {
+             if (dma_ctrl_read(chan, XILINX_DMA_REG_DMASR) &
+                 XILINX_DMA_DMASR_SG_MASK)

why not read this for VDMA too, will it return false?

AFAIK this bit is reserved in VDMA, so reading it can lead to any
random thing.. I would say that potentially it could even be used for
other purposes in future IP releases..

quoted

+                     chan->has_sg = true;
+             dev_dbg(chan->dev, "ch %d: SG %s\n", chan->id,
+                     chan->has_sg ? "enabled" : "disabled");

this debug print can be removed

IMHO if someone will ever enable debug prints for debugging something
and then he/she reports us a log, then it would be useful to see in
the log if the IP was SG or not..

--
~Vinod