linux-kernel - Re: USB mass storage and ARM cache coherency

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Date:	Tue, 16 Feb 2010 08:44:42 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	"Shilimkar, Santosh" <santosh.shilimkar@...com>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Pavel Machek <pavel@....cz>, Greg KH <greg@...ah.com>,
	Matthew Dharm <mdharm-kernel@...-eyed-alien.net>,
	Sergei Shtylyov <sshtylyov@...mvista.com>,
	Ming Lei <tom.leiming@...il.com>,
	Sebastian Siewior <bigeasy@...utronix.de>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	"Mankad, Maulik Ojas" <x0082077@...com>
Subject: Re: USB mass storage and ARM cache coherency

On Tue, Feb 16, 2010 at 01:27:53PM +0530, Shilimkar, Santosh wrote:
> Continuing on the USB issue w.r.t cache coherency, the usb host
> code is violating the buffer ownership rules of streaming APIs from
> dma and non-dma transfers point if view.
> 
> We have a below temporary patch to get around the issue and probably it
> needs to be fixed in the right way in the stack because some controllers
> may not have PIO option even for control transfers. (e.g. Synopsis EHCI
> controller)

        if (usb_endpoint_xfer_control(&urb->ep->desc)
            && !(urb->transfer_flags & URB_NO_SETUP_DMA_MAP)) {
                if (hcd->self.uses_dma) {		<=================
                        urb->setup_dma = dma_map_single(
                                        hcd->self.controller,
                                        urb->setup_packet,
                                        sizeof(struct usb_ctrlrequest),
                                        DMA_TO_DEVICE);

struct usb_hcd *usb_create_hcd (const struct hc_driver *driver,
                struct device *dev, const char *bus_name)
{
...
        hcd->self.uses_dma = (dev->dma_mask != NULL);

Is it easier to make sure that PIO devices don't have dev->dma_mask set?
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