[PATCH v2] dmaengine: dw: Select only supported masters for ACPI devices

[Serge Semin <fancer.lancer@gmail.com>]

The recently submitted fix-commit revealed a problem in the iDMA32
platform code. Even though the controller supported only a single master
the dw_dma_acpi_filter() method hard-coded two master interfaces with IDs
0 and 1. As a result the sanity check implemented in the commit
b336268dde75 ("dmaengine: dw: Add peripheral bus width verification") got
incorrect interface data width and thus prevented the client drivers
from configuring the DMA-channel with the EINVAL error returned. E.g. the
next error was printed for the PXA2xx SPI controller driver trying to
configure the requested channels:

> [  164.525604] pxa2xx_spi_pci 0000:00:07.1: DMA slave config failed
> [  164.536105] pxa2xx_spi_pci 0000:00:07.1: failed to get DMA TX descriptor
> [  164.543213] spidev spi-SPT0001:00: SPI transfer failed: -16

The problem would have been spotted much earlier if the iDMA32 controller
supported more than one master interfaces. But since it supports just a
single master and the iDMA32-specific code just ignores the master IDs in
the CTLLO preparation method, the issue has been gone unnoticed so far.

Fix the problem by specifying a single master ID for both memory and
peripheral devices on the ACPI-based platforms if there is only one master
available on the controller. Thus the issue noticed for the iDMA32
controllers will be eliminated and the ACPI-probed DW DMA controllers will
be configured with the correct master ID by default.

Cc: stable@vger.kernel.org
Fixes: b336268dde75 ("dmaengine: dw: Add peripheral bus width verification")
Fixes: 199244d69458 ("dmaengine: dw: add support of iDMA 32-bit hardware")
Reported-by: Ferry Toth <fntoth@gmail.com>
Closes: https://lore.kernel.org/dmaengine/ZuXbCKUs1iOqFu51@black.fi.intel.com/
Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Closes: https://lore.kernel.org/dmaengine/ZuXgI-VcHpMgbZ91@black.fi.intel.com/
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>

---

Note I haven't got any device with the Intel Merrifield iDMA32 + SPI
PXA2xx pair to test out the solution. So any tests are very welcome. But
based on Andy' (see the reported-by links) and my investigations the fix
seems correct.

Link: https://lore.kernel.org/dmaengine/20240919135854.16124-1-fancer.lancer@gmail.com/
Changelog v2:
- Implement only the "fallback" conditional statement (@Andy)
- Fix incorrect NoF masters literal (@Andy)
- Drop redundant empty line (@Andy)
---
 drivers/dma/dw/acpi.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/dma/dw/acpi.c b/drivers/dma/dw/acpi.c
index c510c109d2c3..806620f5a406 100644
--- a/drivers/dma/dw/acpi.c
+++ b/drivers/dma/dw/acpi.c
@@ -8,6 +8,7 @@
 
 static bool dw_dma_acpi_filter(struct dma_chan *chan, void *param)
 {
+	struct dw_dma *dw = to_dw_dma(chan->device);
 	struct acpi_dma_spec *dma_spec = param;
 	struct dw_dma_slave slave = {
 		.dma_dev = dma_spec->dev,
@@ -17,6 +18,13 @@ static bool dw_dma_acpi_filter(struct dma_chan *chan, void *param)
 		.p_master = 1,
 	};
 
+	/*
+	 * Fallback to using a single interface for both memory and peripheral
+	 * device if there is only one master I/F supported (e.g. iDMA32)
+	 */
+	if (dw->pdata->nr_masters == 1)
+		slave.p_master = 0;
+
 	return dw_dma_filter(chan, &slave);
 }
 
-- 
2.43.0