linux-kernel - RE: [PATCH 2/2] spi: pxa2xx: use a module softdep for dw

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Date:   Thu, 11 Apr 2019 07:14:06 +0000
From:   Flavio Suligoi <f.suligoi@...m.it>
To:     Mark Brown <broonie@...nel.org>
CC:     Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 2/2] spi: pxa2xx: use a module softdep for dw_dmac

> > I think that the problem could be related to how the DMA channel is
> requested.
> > At the moment the function used are:
> 
> > pxa2xx_spi_dma_setup --> dma_request_slave_channel_compat -->
> > --> __dma_request_slave_channel_compat --> dma_request_slave_channel -->
> > --> dma_request_chan
> 
> > Actually the final function "dma_request_chan" return
> > the channel number or "-EPROBE_DEFER" if it's not ready.
> > But this information ("-EPROBE_DEFER") is lost in the penultimate
> function
> > "dma_request_slave_channel", which return only the chann, if all is ok,
> or
> > NULL, in case of errors.
> > So the deferral mechanism is not used.
> 
> Right, yes - that analysis seems correct.  The interfaces seem a bit
> weird here but fixing them looks like the most complete and robust fix.

Ok Mark, I'll fix this problem as soon as I can, using EPROBE_DEFER.
For now, in my application, I use the patch that I already sent,
with the "softdep" workaround:

MODULE_SOFTDEP("pre: dw_dmac");

I tested it a lot, with more than 2000 cold reboot (automatic
switch on/off using a controlled power supply) and it always worked good.

Thanks for your help!

Flavio