linux-kernel - Re: [PATCH] dmaengine: failure to get a specific DMA channel is not critical

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Message-id: <w3pzklcxchm.wl%kuninori.morimoto.gx@renesas.com>
Date:	Tue, 21 Jun 2011 09:19:24 +0900
From:	Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
	Dan Williams <dan.j.williams@...el.com>,
	Vinod Koul <vinod.koul@...el.com>
Subject: Re: [PATCH] dmaengine: failure to get a specific DMA channel is not
 critical


Dear Guennadi, all

> There exist systems with multiple DMA controllers with different
> capabilities. For example, on some sh-mobile / rmobile systems there are
> DMA controllers, whose channels can be configured to be used with
> SD- and MMC-host controllers, serial ports etc. Besides there are also
> DMA controllers, that can only be used for one special function, e.g.,
> for USB. In such cases the DMA client filter function can just choose
> to specify to the DMA driver, which channel it needs. Then the
> .device_alloc_chan_resources() method of the DMA driver will check,
> whether it can provide that dunction. If not, it will fail and the loop
> in __dma_request_channel() will continue to the next DMA device, until
> it finds a suitable one. This works fine with just one minor glitch:
> the kernel logs error messages like
> 
> dmaengine: failed to get <channel name>: (-<error code>)
> 
> after each such non-critical failure. This patch lowers priority of
> this message to the debug level.
> 
> Reported-by: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@....de>
> ---
> 
> Morimoto-san, I don't expect this patch to fail;), but if you like, you 
> could give it a short spin and send your "tested-by" in reply to this 
> mail.

Thanks.
I tested this patch.

I don't know that the dmaengine design,
but this patch remove non-critical error message from USB-DMAC for me.
I tested it on mackerel board + renesas_usbhs + USB-DMAC

Tested-by: Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>

Best regards
--
Kuninori Morimoto
 
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