linux-kernel - Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev

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Date:   Thu, 8 Sep 2016 09:15:36 +0800
From:   Peter Chen <hzpeterchen@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Felipe Balbi <balbi@...nel.org>, Leo Li <pku.leo@...il.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Russell King - ARM Linux <linux@....linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Sekhar Nori <nsekhar@...com>,
        lkml <linux-kernel@...r.kernel.org>,
        Stuart Yoder <stuart.yoder@....com>,
        Scott Wood <oss@...error.net>,
        David Fisher <david.fisher1@...opsys.com>,
        "Thang Q. Nguyen" <tqnguyen@....com>,
        Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent
 dev

On Wed, Sep 07, 2016 at 05:24:08PM +0200, Arnd Bergmann wrote:
> On Wednesday, September 7, 2016 1:24:07 PM CEST Felipe Balbi wrote:
> > 
> > Hi,
> > 
> > Arnd Bergmann <arnd@...db.de> writes:
> > 
> > [...]
> > 
> > > Regarding the DMA configuration that you mention in ci_hdrc_add_device(),
> > > I think we should replace 
> > >
> > >         pdev->dev.dma_mask = dev->dma_mask;
> > >         pdev->dev.dma_parms = dev->dma_parms;
> > >         dma_set_coherent_mask(&pdev->dev, dev->coherent_dma_mask);
> > >
> > > with of_dma_configure(), which has the chance to configure more than
> > > just those three, as the dma API might look into different aspects:
> > >
> > > - iommu specific configuration
> > > - cache coherency information
> > > - bus type
> > > - dma offset
> > > - dma_map_ops pointer
> > >
> > > We try to handle everything in of_dma_configure() at configuration
> > > time, and that would be the place to add anything else that we might
> > > need in the future.
> > 
> > There are a couple problems with this:
> > 
> > 1) won't work for PCI-based systems.
> > 
> > DWC3 is used in production PCI-based HW and also in Synopsys HAPS DX
> > platform (FPGA that appears like a PCI card to host PC)
> 
> Right, I was specifically talking about the code in chipidea here,
> which I think is never used on the PCI bus, and how the current
> code is broken. We can probably do better than of_dma_configure()
> (see below), but it would be an improvement.

Chipidea is also used at PCI bus too, see drivers/usb/chipidea/ci_hdrc_pci.c

-- 

Best Regards,
Peter Chen