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

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Date:	Fri, 18 Mar 2016 03:25:41 +0000
From:	Rajesh Bhagat <rajesh.bhagat@....com>
To:	Peter Chen <hzpeterchen@...il.com>, Arnd Bergmann <arnd@...db.de>
CC:	Li Yang <leoli@...escale.com>,
	Bjorn Andersson <bjorn.andersson@...aro.org>,
	Peter Chen <peter.chen@....com>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	"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



> -----Original Message-----
> From: Peter Chen [mailto:hzpeterchen@...il.com]
> Sent: Friday, March 18, 2016 7:24 AM
> To: Arnd Bergmann <arnd@...db.de>
> Cc: Li Yang <leoli@...escale.com>; Bjorn Andersson <bjorn.andersson@...aro.org>;
> Peter Chen <peter.chen@....com>; Greg Kroah-Hartman
> <gregkh@...uxfoundation.org>; Rajesh Bhagat <rajesh.bhagat@....com>; 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
> Subject: Re: [PATCH] usb: chipidea: Configure DMA properties and ops from DT
> 
> On Thu, Mar 17, 2016 at 04:52:55PM +0100, Arnd Bergmann wrote:
> > On Monday 14 March 2016 18:51:08 Peter Chen wrote:
> > > 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:
> > > > >
> > > > > 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.
> > >
> >
> > I don't think it's a very widespread problem, there are only very few
> > developers that intentionally use this method, and some use the
> > platform_device_register_full() call to create a device with a known
> > mask, which is generally ok for the limited case where the driver is
> > only ever going to run on a single platform, but not in the more
> > general case that of_dma_configure is designed to handle.
> 
> Even only for qualcomm platforms, it may be possible have different DMA masks at
> ARM64 platforms, so we may can't use a fixed value at glue layer driver. So, using
> of_dma_configure is suitable choice for DT platforms for this case, right?
> 
> >
> > I think we should fix the drivers to consistently use the device that
> > was created by the platform (DT or ACPI or board file) to pass that
> > into the DMA API, anything else will just cause more subtle bugs.
> >
> 
> Although I don't know what kinds of bugs it may have, it may be met before,
> otherwise, why most of platform drivers need to call dma_set_coherent_mask or
> dma_coerce_mask_and_coherent explicitly
> 
> --
> 
> Best Regards,
> Peter Chen

Though chipidea platform drivers are calling functions mentioned by you i.e. dma_set_coherent_mask
or dma_coerce_mask_and_coherent explicity e.g. in file drivers/usb/chipidea/ci_hdrc_imx.c. 

Still the mentioned error is coming while calling ci_hdrc_add_device which lies in chipidea/core.c. similar is 
the case with DWC3 driver. 

Best Regards,
Rajesh Bhagat