linux-kernel - Re: [PATCH v2] ARM: dts: imx6dl: disable dma support for spi on i.mx6dl

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Message-ID: <1410945574.2731.3.camel@pengutronix.de>
Date:	Wed, 17 Sep 2014 11:19:34 +0200
From:	Lucas Stach <l.stach@...gutronix.de>
To:	Robin Gong <b38343@...escale.com>
Cc:	mark.rutland@....com, devicetree@...r.kernel.org,
	linux@....linux.org.uk, pawel.moll@....com,
	ijc+devicetree@...lion.org.uk, linux-kernel@...r.kernel.org,
	robh+dt@...nel.org, shawn.guo@...escale.com, kernel@...gutronix.de,
	galak@...eaurora.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] ARM: dts: imx6dl: disable dma support for spi on
 i.mx6dl

Am Mittwoch, den 17.09.2014, 17:19 +0800 schrieb Robin Gong:
> On Wed, Sep 17, 2014 at 10:55:56AM +0200, Lucas Stach wrote:
> > Am Mittwoch, den 17.09.2014, 16:41 +0800 schrieb Robin Gong:
> > > On Tue, Sep 16, 2014 at 11:50:06AM +0200, Lucas Stach wrote:
> > > > Hi Robin,
> > > > 
> > > > Am Dienstag, den 16.09.2014, 11:41 +0800 schrieb Robin Gong:
> > > > > Hi Lucas,
> > > > >   I understood your concern,but looks we have to break old DT.
> > > > 
> > > > Sorry, but this isn't going to happen. And honestly I don't even see the
> > > > need to do so.
> > > > 
> > > > > Our old DT
> > > > > support SPI DMA on i.mx6q/dl(v2,b3810c3dc1bcbc6a), but the DMA support patch
> > > > > for SPI driver is still in reviewing(v6).
> > > > 
> > > > So this means now is the time to fix this driver patch to not enable DMA
> > > > on imx6dl. Nobody will experience any breakage in this case.
> > > >
> > > Sorry, i.mx6q and i.mx6dl are totally same, not only IP but also clock. So we
> > > can't distinguish them except for different compatible name....
> > 
> > I know that, but I still don't see the problem.
> > 
> > If this issue is specific to the ECSPI IP integrated into a imx6dl SoC
> > you need to check for the machine compatible in the driver and disable
> > DMA support based on this. We generally avoid checking for the machine
> > compatible in drivers and prefer to have a specific IP block compatible
> > instead, but in that case it's the only reasonable thing to do.
> > 
> > Regards,
> > Lucas
> Sounds we make a agreement on use different compatible name, right? I will
> make patch for reviewing, thanks.

No you can't use a new compatible name for the IP block, as this again
would only fix things for users with new devicetrees. Also this has
nothing to do with the IP block, but is an integration issue between
ECPSI and imx6dl.

So what you need to do is something like this in the ecspi kernel
driver:

if (of_machine_is_compatible("fsl,imx6dl") {
    do_whatever_is_necessary_to_make_sure_DMA_is_not_enabled();
}

Regards,
Lucas
-- 
Pengutronix e.K.             | Lucas Stach                 |
Industrial Linux Solutions   | http://www.pengutronix.de/  |

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