On Thu, Sep 19, 2024 at 06:14:06PM +0300, Andy Shevchenko wrote:
On Thu, Sep 19, 2024 at 04:58:14PM +0300, Serge Semin wrote:
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.
...
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, .src_id = dma_spec->slave_id, .dst_id = dma_spec->slave_id, .m_master = 0,
.p_master = 1,
I would leave this line as is and it makes more consistent in my opinion with the below comments which starts with the words "Fallback to...".
Ok.
};
- /*
* 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 == 0)
Why '== 0' and not '== 1'? Or '>= 2' if you wish to be on the save side (however, that '== 0' case is not obvious to me — do we really have that IRL?).
I several times checked the patch and never noticed this obvious typo. Indeed nr_masters is the actual number of masters. So the statement should have been '== 1'.
slave.p_master = 0;- else
slave.p_master = 1;
One blank line is enough.
Fully agreed.
I guess I was too hurrying to submit the fix so missed two stupid mistakes in just 7-lines patch. "Nice" anti-record for me. Sorry about that and much appreciated for reviewing the bit. I'll resubmit v2 shortly.
-Serge(y)
return dw_dma_filter(chan, &slave); }
...
P.S. I'll test it later this or next week, if Ferry wouldn't beat me up to it.
-- With Best Regards, Andy Shevchenko