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

[Andy Shevchenko]

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...".

>  	};
>  
> +	/*
> +	 * 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?).

> +		slave.p_master = 0;
> +	else
> +		slave.p_master = 1;

> +
> +

One blank line is enough.

>  	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