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

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Date:   Wed, 10 Apr 2019 14:05:38 +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

Hi Mark,

> On Wed, Apr 10, 2019 at 02:51:36PM +0200, Flavio Suligoi wrote:
> > With dw_dmac, sometimes the request of a DMA channel fails because
> > the DMA driver is not ready, so an explicit dependency request
> > is necessary.
> 
> While this isn't going to hurt anything and might actually help so it's
> fine doesn't this also suggest that there's an issue with deferred probe
> going on as well?

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.

Flavio