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

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Message-ID: <5844875.KucAoPMrXi@wuerfel>
Date:   Tue, 06 Sep 2016 12:38:29 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Peter Chen <hzpeterchen@...il.com>
Cc:     Leo Li <pku.leo@...il.com>, Felipe Balbi <balbi@...nel.org>,
        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 Tuesday, September 6, 2016 2:35:29 PM CEST Peter Chen wrote:
> On Mon, Sep 05, 2016 at 05:39:27PM +0200, Arnd Bergmann wrote:
> > On Friday, September 2, 2016 5:16:31 PM CEST Leo Li wrote:

> > 
> > Most of these are probably never used with any nonstandard
> > DMA settings (IOMMU, cache coherency, offset, ...).
> > 
> > One thing we could possibly do is to go through these and
> > replace the hardcoded dma mask setup with of_dma_configure()
> > in all cases in which we actually use DT for probing, which
> > should cover the interesting cases.
> > 
> 
> One case I am going to work is to let USB chipidea driver support iommu,
> the chipidea core device is no of_node, and created by
> platform_add_device on the runtime. Using of_dma_configure with parent
> of_node is a solution from my point, like [1].
> 
> https://lkml.org/lkml/2016/2/22/7

Right, that should make it work with iommu as well. However, it does
not solve the other issue I mentioned above, with boards that have
USB devices hardwired to a chipidea host controller that need
configuration from DT. For that, we still need to come up with another
way to associate the DT hierarchy in the host bridge node with
the Linux platform_device.

	Arnd