linux-kernel - RE: [PATCH v5 1/2] i2c: add DMA support for freescale i2c driver

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Message-ID: <1a4d2e9ddc67421d8588305c927f3d3d@BL2PR03MB338.namprd03.prod.outlook.com>
Date:	Thu, 31 Jul 2014 06:16:55 +0000
From:	Yao Yuan <yao.yuan@...escale.com>
To:	Marek Vasut <marex@...x.de>,
	Lothar Waßmann <LW@...o-electronics.de>
CC:	Varka Bhadram <varkabhadram@...il.com>,
	"wsa@...-dreams.de" <wsa@...-dreams.de>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
Subject: RE: [PATCH v5 1/2] i2c: add DMA support for freescale i2c driver

Marek Vasut wrote:
> On Wednesday, July 23, 2014 at 02:15:02 PM, Lothar Waßmann wrote:
> > Hi,
> >
> > Varka Bhadram wrote:
> > > On 07/23/2014 04:41 PM, Yao Yuan wrote:
> > > > Hi,
> > > >
> > > > Thanks for your review.
> > > >
> > > > Lothar Waßmann wrote:
> > > >> Yuan Yao wrote:
> > > >>> Add dma support for i2c. This function depend on DMA driver.
> > > >>> You can turn on it by write both the dmas and dma-name
> > > >>> properties in dts node.
> > > >>>
> > > >>> Signed-off-by: Yuan Yao <yao.yuan@...escale.com>
> > > >>> ---
> > > >>>
> > > >>>   drivers/i2c/busses/i2c-imx.c | 377
> > > >
> > > > [...]
> > > >
> > > >>> +
> > > >>> +fail_rx:
> > > >>> +	dma_release_channel(dma->chan_rx);
> > > >>> +fail_tx:
> > > >>> +	dma_release_channel(dma->chan_tx);
> > > >>> +fail_al:
> > > >>> +	devm_kfree(dev, dma);
> > > >>
> > > >> No need for this one (that's the whole point of using devm_kzalloc())!
> > > >
> > > > When DMA request failed, I2C will switch to PIO mode. So if the
> > > > failed reason is just like DMA channel request failed. At this
> > > > time the DMA should free by devm_kfree(). Is it?
> > >
> > > If probe failed the memory will be freed automatically because we
> > > are using devm_kzalloc()...
> > >
> > > If we use devm_kzalloc() ,no need to free manually on fail...
> >
> > Yes, but as Yuan Yao stated, the driver will still work without DMA
> > but carry around the unecessary allocated imx_i2c_dma struct.
> > The devm_kfree() is not in the failure path of the driver's probe()
> > function, but in the function that tries to initialize the optional
> > DMA support.
> 
> If the DMA fails, I'd just make the entire probe fail. In case you cannot probe
> DMA for your hardware, which is exected to be DMA capable, it means
> something is wrong anyway.

Yes, but if there is something wrong in dma, I think the i2c is innocent. So I think the error message is necessary but i2c can continue work.


Best regards,
Yuan Yao
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