linux-kernel - Re: [PATCH] usb: chipidea: Configure DMA properties and ops from DT

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Date:	Mon, 14 Mar 2016 18:51:08 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Li Yang <leoli@...escale.com>
Cc:	Bjorn Andersson <bjorn.andersson@...aro.org>,
	Peter Chen <Peter.Chen@....com>, Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Rajesh Bhagat <rajesh.bhagat@....com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	linux-arm-msm <linux-arm-msm@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] usb: chipidea: Configure DMA properties and ops from DT

On Wed, Mar 09, 2016 at 05:16:50PM -0600, Li Yang wrote:
> On Tue, Mar 8, 2016 at 9:40 PM, Bjorn Andersson
> <bjorn.andersson@...aro.org> wrote:
> > On Tue, Mar 8, 2016 at 11:52 AM, Li Yang <leoli@...escale.com> wrote:
> >> On Wed, Mar 2, 2016 at 4:59 PM, Li Yang <leoli@...escale.com> wrote:
> >>> On Mon, Feb 22, 2016 at 4:07 PM, Bjorn Andersson
> >>> <bjorn.andersson@...aro.org> wrote:
> >>>> On Mon 22 Feb 02:03 PST 2016, Srinivas Kandagatla wrote:
> >>>>
> >>>>>
> >>>>>
> >>>>> On 22/02/16 05:32, Bjorn Andersson wrote:
> >>>>> >On certain platforms (e.g. ARM64) the dma_ops needs to be explicitly set
> >>>>> >to be able to do DMA allocations, so use the of_dma_configure() helper
> >>>>> >to populate the dma properties and assign an appropriate dma_ops.
> > [..]
> >>>>> None of the drivers call of_dma_configure() explicitly, which makes me feel
> >>>>> that we are doing something wrong. TBH, this should be handled in more
> >>>>> generic way rather than driver like this having an explicit call to
> >>>>> of_dma_configure().
> >>>>>
> >>>>
> >>>> I agree, trying to figure out if it should be inherited or something.
> >>>
> >>> I also agree.  We need address it in a more generic way.  I did a
> >>> search for platform_device_add()/platform_device_register() in the
> >>> kernel source code.  I found a lot of them and many could be also
> >>> doing DMA.  Looks like it is still too early to assume every device is
> >>> already getting dma_ops set through bus probe.  Otherwise, many
> >>> drivers are potentially broken by this assumption.
> >>
> >> Any further comment on this topic?  I added the linux-arm mailing list
> >> which was missing from previous discussion.
> >>
> >
> > I had the chance to go through this with Arnd and the verdict is that
> > devices not described in DT should not do DMA (or allocate buffers for
> > doing DMA).
> >
> > So I believe the solution is to fall back on Peter's description; the
> > chipidea driver is the core driver and the Qualcomm code should just
> > be a platform layer.
> >
> > My suggestion is that we turn the chipidea core into a set of APIs
> > that can called by the platform specific pieces. That way we will have
> > the chipidea core be the device described in the DT.
> 
> But like I said, this problem is not just existing for chipidea
> driver.  We already found that the dwc3 driver is also suffering from
> the same issue.  I don't know how many other drivers are impacted by
> this change, but I suspect there will be some. A grep of
> platform_device_add() in driver/ directory returns many possible
> drivers to be impacted.  As far as I know, the
> drivers/net/ethernet/freescale/fman/mac.c is registering child
> ethernet devices that definitely will do dma.   If you want to do this
> kind of rework to all these drivers, it will be a really big effort.
> 

+1

Yes, I think this DMA things should be covered by driver core too.

-- 

Best Regards,
Peter Chen