linux-kernel - Re: [PATCH 3/4] dmaengine: core: Introduce new, universal API to request a channel

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Message-ID: <4696298.Uj40YldTVN@wuerfel>
Date:	Thu, 03 Dec 2015 16:45:38 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
Cc:	vinod.koul@...el.com, andy.shevchenko@...il.com,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	nsekhar@...com, tony@...mide.com
Subject: Re: [PATCH 3/4] dmaengine: core: Introduce new, universal API to request a channel

On Thursday 03 December 2015 17:42:31 Peter Ujfalusi wrote:
> > 
> >> +       if (chan) {
> >> +               /* Valid channel found */
> >> +               if (!IS_ERR(chan) || PTR_ERR(chan) == -EPROBE_DEFER)
> >> +                       return chan;
> >> +
> >> +               pr_warn("%s: %s DMA request failed, falling back to legacy\n",
> >> +                       __func__, dev->of_node ? "OF" : "ACPI");
> >> +       }
> > 
> > Maybe print the error code as well?
> 
> Or remove the print altogether?
> In a healthy system we will either get the channel or the EPROBE_DEFER, in
> case of the platforms where the DT lookup does not work we expect errors and
> it is 'normal'.
> I think if we fail via DT/ACPI and we fail with legacy also then the client
> driver will say something about it anyways, or deal with it as it see fits.
> 

Right, that works too. It took me a while to figure out that we only get
there on systems that have ACPI or DT enabled for a particular device,
but where the normal method failed, rather than also systems with traditional
board files. Without the pr_warn, I would not have needed to think about
this ;-)

	Arnd
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