linux-kernel - Re: [PATCH v2 03/15] dmaengine: Add no_wakeup parameter to dmaengine_prep_dma

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <5052D979.3030901@ti.com>
Date:	Fri, 14 Sep 2012 10:15:05 +0300
From:	Peter Ujfalusi <peter.ujfalusi@...com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Lars-Peter Clausen <lars@...afoo.de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Liam Girdwood <lrg@...com>, Tony Lindgren <tony@...mide.com>,
	Vinod Koul <vinod.koul@...el.com>, Dan Williams <djbw@...com>,
	Jarkko Nikula <jarkko.nikula@...mer.com>,
	alsa-devel@...a-project.org, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Janusz Krzysztofik <jkrzyszt@....icnet.pl>,
	Ricardo Neri <ricardo.neri@...com>
Subject: Re: [PATCH v2 03/15] dmaengine: Add no_wakeup parameter to dmaengine_prep_dma_cyclic()

On 09/13/2012 06:38 PM, Russell King - ARM Linux wrote:
> On Thu, Sep 13, 2012 at 05:27:09PM +0200, Lars-Peter Clausen wrote:
>> Hm... Do you think it would work as well if we implement this by setting the
>> callback for the descriptor to NULL? If the callback is NULL there is
>> nothing to at the end of a transfer/period and the dma engine driver may
>> choose to disable interrupts. This would also benefit non cyclic transfers
>> where the callback is NULL and we do not need add the new parameter to
>> dmaengine_prep_dma_cyclic.
> 
> Actually, there's a way to do that already.  DMA_PREP_INTERRUPT.
> Unfortunately, most DMA engine slave API users don't set it when they
> setup their transfer:
> 
>  * @DMA_PREP_INTERRUPT - trigger an interrupt (callback) upon completion of
>  *  this transaction

As I mentioned already to Vinod: the description of this flag is close enough
for our needs (other than the notion of 'this transaction' is not really
correct for cyclic mode).
I will resend the series to add the flags as new parameter instead of the
no_wakeup.

> 
> if we fixed that, then we could use the lack of it to avoid the interrupt.
> 
> However, cyclic transfers don't have the flags parameter used to pass this
> bit.  Yet another bit of yucky inconsistent design in DMA engine land...
> 


-- 
Péter
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/