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

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Date:	Wed, 17 Feb 2010 12:02:21 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Shilimkar, Santosh" <santosh.shilimkar@...com>
cc:	Oliver Neukum <oliver@...kum.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	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>,
	"Gadiyar, Anand" <gadiyar@...com>
Subject: RE: USB mass storage and ARM cache coherency

On Wed, 17 Feb 2010, Shilimkar, Santosh wrote:

> How about below approach? Controller driver can set 
> "uses_pio_for_control" if it can't do dma for control transfer.
> 
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index 80995ef..e3eae02 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -1276,7 +1276,7 @@ static int map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
>  
>  	if (usb_endpoint_xfer_control(&urb->ep->desc)
>  	    && !(urb->transfer_flags & URB_NO_SETUP_DMA_MAP)) {
> -		if (hcd->self.uses_dma) {
> +		if (hcd->self.uses_dma && !hcd->self.uses_pio_for_control) {
>  			urb->setup_dma = dma_map_single(
>  					hcd->self.controller,
>  					urb->setup_packet,
> @@ -1335,7 +1335,7 @@ static void unmap_urb_for_dma(struct usb_hcd *hcd, struct urb *urb)
>  
>  	if (usb_endpoint_xfer_control(&urb->ep->desc)
>  	    && !(urb->transfer_flags & URB_NO_SETUP_DMA_MAP)) {
> -		if (hcd->self.uses_dma)
> +		if (hcd->self.uses_dma && !hcd->self.uses_pio_for_control)
>  			dma_unmap_single(hcd->self.controller, urb->setup_dma,
>  					sizeof(struct usb_ctrlrequest),
>  					DMA_TO_DEVICE);
> diff --git a/include/linux/usb.h b/include/linux/usb.h
> index d7ace1b..ba5b0a2 100644
> --- a/include/linux/usb.h
> +++ b/include/linux/usb.h
> @@ -329,6 +329,9 @@ struct usb_bus {
>  	int busnum;			/* Bus number (in order of reg) */
>  	const char *bus_name;		/* stable id (PCI slot_name etc) */
>  	u8 uses_dma;			/* Does the host controller use DMA? */
> +	u8 uses_pio_for_control;	/* Does the host controller use PIO
> +					 * for control tansfers? 
> +					 */
>  	u8 otg_port;			/* 0, or number of OTG/HNP port */
>  	unsigned is_b_host:1;		/* true during some HNP roleswitches */
>  	unsigned b_hnp_enable:1;	/* OTG: did A-Host enable HNP? */

Why do you skip mapping the setup packet but not the data packet?

Alan Stern

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