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

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Date:   Thu, 08 Sep 2016 12:43:06 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Peter Chen <hzpeterchen@...il.com>, 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\@vger.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\@lists.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev


Hi,

Arnd Bergmann <arnd@...db.de> writes:
> On Thursday, September 8, 2016 11:29:04 AM CEST Felipe Balbi wrote:
>> > If we do that, we have to put child devices of the dwc3 devices into
>> > the platform glue, and it also breaks those dwc3 devices that don't
>> > have a parent driver.
>> 
>> Well, this is easy to fix:
>> 
>>         if (dwc->dev->parent) {
>>                 dwc->sysdev = dwc->dev->parent;
>>         } else {
>>                 dev_info(dwc->dev, "Please provide a glue layer!\n");
>>                 dwc->sysdev = dwc->dev;
>>         }
>
> I don't understand. Do you mean we should have an extra level of
> stacking and splitting "static struct platform_driver dwc3_driver"
> in two so instead of
>
> 	"qcom,dwc3" -> "snps,dwc3" (usb_bus.sysdev) -> "xhci" (usb_bus.dev)
>
> we do this?
>
> 	"qcom,dwc3" -> "snps,dwc3" (usb_bus.sysdev) -> "dwc3-glue" -> "xhci" (usb_bus.dev)

no :-)

If we have a parent device, use that as sysdev, otherwise use self as
sysdev.

> That sounds a bit clumsy for the sake of consistency with PCI.
> The advantage is that xhci can always use the grandparent device
> as sysdev whenever it isn't probed through PCI or firmware
> itself, but the purpose of the dwc3-glue is otherwise questionable.
>
> How about adding a 'compatible="snps,dwc3-pci"' property for the dwc3
> device when that is created from the PCI driver and checking for that
> with the device property interface instead? If it's "snps,dwc3"
> we use the device itself while for "snps,dwc3-pci", we use the parent?

Any reason why we wouldn't use e.g. dwc3-omap.dev as sysdev?

-- 
balbi

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