linux-kernel - Re: [PATCH v5 4/6] usb: xhci: use bus->sysdev for DMA configuration

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Message-ID: <Pine.LNX.4.44L0.1701111008240.1900-100000@iolanthe.rowland.org>
Date:   Wed, 11 Jan 2017 10:08:42 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>
cc:     Sriram Dash <sriram.dash@....com>, <linux-kernel@...r.kernel.org>,
        <linux-usb@...r.kernel.org>, <mathias.nyman@...el.com>,
        <gregkh@...uxfoundation.org>, <suresh.gupta@....com>,
        <felipe.balbi@...ux.intel.com>, <pku.leo@...il.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v5 4/6] usb: xhci: use bus->sysdev for DMA configuration

On Wed, 11 Jan 2017, Mathias Nyman wrote:

> On 17.11.2016 13:43, Sriram Dash wrote:
> > From: Arnd Bergmann <arnd@...db.de>
> >
> > For xhci-hcd platform device, all the DMA parameters are not
> > configured properly, notably dma ops for dwc3 devices. So, set
> > the dma for xhci from sysdev. sysdev is pointing to device that
> > is known to the system firmware or hardware.
> >
> > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > Signed-off-by: Sriram Dash <sriram.dash@....com>
> > Tested-by: Baolin Wang <baolin.wang@...aro.org>
> > ---
> 
> ...
> 
> > +	/*
> > +	 * sysdev must point to a device that is known to the system firmware
> > +	 * or PCI hardware. We handle these three cases here:
> > +	 * 1. xhci_plat comes from firmware
> > +	 * 2. xhci_plat is child of a device from firmware (dwc3-plat)
> > +	 * 3. xhci_plat is grandchild of a pci device (dwc3-pci)
> > +	 */
> > +	sysdev = &pdev->dev;
> > +	if (sysdev->parent && !sysdev->of_node && sysdev->parent->of_node)
> > +		sysdev = sysdev->parent;
> > +#ifdef CONFIG_PCI
> > +	else if (sysdev->parent && sysdev->parent->parent &&
> > +		 sysdev->parent->parent->bus == &pci_bus_type)
> > +		sysdev = sysdev->parent->parent;
> > +#endif
> > +
> 
> Not maybe the the ideal situation here, and looks really tailored to make PCI dwc3
> controllers with xhci support work.
> 
> Was there some reason child devices can't automatically inherit the dma mask from the parents,
> forcing us to dig it from grandparents?
> 
> Anyway, looks like the dwc3 part is already in 4.10-rc,
> If Greg and Alan want to take this series that's fine by me

I have no objections.

Alan Stern

> I haven't tested that it won't break anything on PCI XHCI controllers though
> 
> -Mathias