From: Robin Gong <b38343@freescale.com>
To: Mark Brown <broonie@kernel.org>
Cc: <linux-arm-kernel@lists.infradead.org>,
<linux-spi@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<marex@denx.de>, <shawn.guo@linaro.org>, <Frank.Li@freescale.com>
Subject: Re: [PATCH v5] spi: spi-imx: add DMA support
Date: Thu, 11 Sep 2014 09:37:38 +0800 [thread overview]
Message-ID: <20140911013737.GA366@Robin-OptiPlex-780> (raw)
In-Reply-To: <20140910155216.GI7960@sirena.org.uk>
On Wed, Sep 10, 2014 at 04:52:16PM +0100, Mark Brown wrote:
> On Wed, Sep 10, 2014 at 11:18:01PM +0800, Robin Gong wrote:
> > On Wed, Sep 10, 2014 at 12:45:30PM +0100, Mark Brown wrote:
>
> > > > Yes, you're right. I should use "transfer->tx_sg->sgl == NULL" or
> > > > "transfer->rx_sg->sgl == NULL" instead of usedma flag in driver, right?
>
> > > Right.
>
> > But looks spi core framework can make sure every rx or tx transfer in sequence.
> > If so, can_dma will never be called until this transfer finished
> > (spi_pump_messages), and my usedma flag also never be modified until next
> > transfer start. Please correct me if I am wrong, thanks.
>
> Even if that were true currently this would still not be good code since
> it would break in the face of SPI core changes. In any case the
> assumption isn't true for the current SPI core, the DMA mapping is done
> for all transfers in a message before we start running them and it's
> entirely likely that we will have patterns like a short PIO transfer
> followed by a big data block.
Understood, will improve it in v6.Thanks.
prev parent reply other threads:[~2014-09-11 1:37 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-10 1:30 [PATCH v5] spi: spi-imx: add DMA support Robin Gong
2014-09-10 4:16 ` Varka Bhadram
[not found] ` <540FD084.6000805-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2014-09-10 5:46 ` Robin Gong
[not found] ` <1410312604-31949-1-git-send-email-b38343-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
2014-09-10 8:17 ` Arnd Bergmann
2014-09-10 8:28 ` Robin Gong
2014-09-10 10:21 ` Mark Brown
[not found] ` <20140910102105.GR2601-GFdadSzt00ze9xe1eoZjHA@public.gmane.org>
2014-09-10 11:22 ` Robin Gong
2014-09-10 11:45 ` Mark Brown
[not found] ` <20140910114530.GD7960-GFdadSzt00ze9xe1eoZjHA@public.gmane.org>
2014-09-10 15:18 ` Robin Gong
2014-09-10 15:52 ` Mark Brown
2014-09-11 1:37 ` Robin Gong [this message]
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