[PATCH AUTOSEL 5.4 78/80] dmaengine: dw: Add DMA-channels mask cell support

[PATCH AUTOSEL 5.4 78/80] dmaengine: dw: Add DMA-channels mask cell support

[Sasha Levin]

From: Serge Semin <Sergey.Semin@baikalelectronics.ru>

[ Upstream commit e8ee6c8cb61b676f1a2d6b942329e98224bd8ee9 ]

DW DMA IP-core provides a way to synthesize the DMA controller with
channels having different parameters like maximum burst-length,
multi-block support, maximum data width, etc. Those parameters both
explicitly and implicitly affect the channels performance. Since DMA slave
devices might be very demanding to the DMA performance, let's provide a
functionality for the slaves to be assigned with DW DMA channels, which
performance according to the platform engineer fulfill their requirements.
After this patch is applied it can be done by passing the mask of suitable
DMA-channels either directly in the dw_dma_slave structure instance or as
a fifth cell of the DMA DT-property. If mask is zero or not provided, then
there is no limitation on the channels allocation.

For instance Baikal-T1 SoC is equipped with a DW DMAC engine, which first
two channels are synthesized with max burst length of 16, while the rest
of the channels have been created with max-burst-len=4. It would seem that
the first two channels must be faster than the others and should be more
preferable for the time-critical DMA slave devices. In practice it turned
out that the situation is quite the opposite. The channels with
max-burst-len=4 demonstrated a better performance than the channels with
max-burst-len=16 even when they both had been initialized with the same
settings. The performance drop of the first two DMA-channels made them
unsuitable for the DW APB SSI slave device. No matter what settings they
are configured with, full-duplex SPI transfers occasionally experience the
Rx FIFO overflow. It means that the DMA-engine doesn't keep up with
incoming data pace even though the SPI-bus is enabled with speed of 25MHz
while the DW DMA controller is clocked with 50MHz signal. There is no such
problem has been noticed for the channels synthesized with
max-burst-len=4.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Link: https://lore.kernel.org/r/20200731200826.9292-6-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/dma/dw/core.c                | 4 ++++
 drivers/dma/dw/of.c                  | 7 +++++--
 include/linux/platform_data/dma-dw.h | 2 ++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index a1b56f52db2f2..5e7fdc0b6e3db 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -772,6 +772,10 @@ bool dw_dma_filter(struct dma_chan *chan, void *param)
 	if (dws->dma_dev != chan->device->dev)
 		return false;
 
+	/* permit channels in accordance with the channels mask */
+	if (dws->channels && !(dws->channels & dwc->mask))
+		return false;
+
 	/* We have to copy data since dws can be temporary storage */
 	memcpy(&dwc->dws, dws, sizeof(struct dw_dma_slave));
 
diff --git a/drivers/dma/dw/of.c b/drivers/dma/dw/of.c
index 9e27831dee324..43e975fb67142 100644
--- a/drivers/dma/dw/of.c
+++ b/drivers/dma/dw/of.c
@@ -22,18 +22,21 @@ static struct dma_chan *dw_dma_of_xlate(struct of_phandle_args *dma_spec,
 	};
 	dma_cap_mask_t cap;
 
-	if (dma_spec->args_count != 3)
+	if (dma_spec->args_count < 3 || dma_spec->args_count > 4)
 		return NULL;
 
 	slave.src_id = dma_spec->args[0];
 	slave.dst_id = dma_spec->args[0];
 	slave.m_master = dma_spec->args[1];
 	slave.p_master = dma_spec->args[2];
+	if (dma_spec->args_count >= 4)
+		slave.channels = dma_spec->args[3];
 
 	if (WARN_ON(slave.src_id >= DW_DMA_MAX_NR_REQUESTS ||
 		    slave.dst_id >= DW_DMA_MAX_NR_REQUESTS ||
 		    slave.m_master >= dw->pdata->nr_masters ||
-		    slave.p_master >= dw->pdata->nr_masters))
+		    slave.p_master >= dw->pdata->nr_masters ||
+		    slave.channels >= BIT(dw->pdata->nr_channels)))
 		return NULL;
 
 	dma_cap_zero(cap);
diff --git a/include/linux/platform_data/dma-dw.h b/include/linux/platform_data/dma-dw.h
index f3eaf9ec00a1b..70078be166e3c 100644
--- a/include/linux/platform_data/dma-dw.h
+++ b/include/linux/platform_data/dma-dw.h
@@ -21,6 +21,7 @@
  * @dst_id:	dst request line
  * @m_master:	memory master for transfers on allocated channel
  * @p_master:	peripheral master for transfers on allocated channel
+ * @channels:	mask of the channels permitted for allocation (zero value means any)
  * @hs_polarity:set active low polarity of handshake interface
  */
 struct dw_dma_slave {
@@ -29,6 +30,7 @@ struct dw_dma_slave {
 	u8			dst_id;
 	u8			m_master;
 	u8			p_master;
+	u8			channels;
 	bool			hs_polarity;
 };
 
-- 
2.25.1

[PATCH AUTOSEL 5.4 79/80] dmaengine: dw: Activate FIFO-mode for memory peripherals only

[Sasha Levin]

From: Serge Semin <Sergey.Semin@baikalelectronics.ru>

[ Upstream commit 6d9459d04081c796fc67c2bb771f4e4ebb5744c4 ]

CFGx.FIFO_MODE field controls a DMA-controller "FIFO readiness" criterion.
In other words it determines when to start pushing data out of a DW
DMAC channel FIFO to a destination peripheral or from a source
peripheral to the DW DMAC channel FIFO. Currently FIFO-mode is set to one
for all DW DMAC channels. It means they are tuned to flush data out of
FIFO (to a memory peripheral or by accepting the burst transaction
requests) when FIFO is at least half-full (except at the end of the block
transfer, when FIFO-flush mode is activated) and are configured to get
data to the FIFO when it's at least half-empty.

Such configuration is a good choice when there is no slave device involved
in the DMA transfers. In that case the number of bursts per block is less
than when CFGx.FIFO_MODE = 0 and, hence, the bus utilization will improve.
But the latency of DMA transfers may increase when CFGx.FIFO_MODE = 1,
since DW DMAC will wait for the channel FIFO contents to be either
half-full or half-empty depending on having the destination or the source
transfers. Such latencies might be dangerous in case if the DMA transfers
are expected to be performed from/to a slave device. Since normally
peripheral devices keep data in internal FIFOs, any latency at some
critical moment may cause one being overflown and consequently losing
data. This especially concerns a case when either a peripheral device is
relatively fast or the DW DMAC engine is relatively slow with respect to
the incoming data pace.

In order to solve problems, which might be caused by the latencies
described above, let's enable the FIFO half-full/half-empty "FIFO
readiness" criterion only for DMA transfers with no slave device involved.
Thanks to the commit 99ba8b9b0d97 ("dmaengine: dw: Initialize channel
before each transfer") we can freely do that in the generic
dw_dma_initialize_chan() method.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200731200826.9292-3-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/dma/dw/dw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/dma/dw/dw.c b/drivers/dma/dw/dw.c
index 7a085b3c1854c..d9810980920a1 100644
--- a/drivers/dma/dw/dw.c
+++ b/drivers/dma/dw/dw.c
@@ -14,7 +14,7 @@
 static void dw_dma_initialize_chan(struct dw_dma_chan *dwc)
 {
 	struct dw_dma *dw = to_dw_dma(dwc->chan.device);
-	u32 cfghi = DWC_CFGH_FIFO_MODE;
+	u32 cfghi = is_slave_direction(dwc->direction) ? 0 : DWC_CFGH_FIFO_MODE;
 	u32 cfglo = DWC_CFGL_CH_PRIOR(dwc->priority);
 	bool hs_polarity = dwc->dws.hs_polarity;
 
-- 
2.25.1