linux-kernel - Re: [PATCH 1/1] usb: xhci: setup packets don't need DMA mapping

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Date:   Mon, 18 Jan 2021 10:07:17 +0900
From:   Daewoong Kim <daewoong00.kim@....com>
To:     hzpeterchen@...il.com
Cc:     b-liu@...com, allen.lkml@...il.com, gustavoars@...nel.org,
        a.darwish@...utronix.de, romain.perier@...il.com,
        dvyukov@...gle.com, andreyknvl@...gle.com, mathias.nyman@...el.com,
        gregkh@...uxfoundation.org, neidhard.kim@....com,
        raxis.lim@....com, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH 1/1] usb: xhci: setup packets don't need DMA mapping

Peter Chen, thanks for your comments.

On Fri, 15 Jan 2021 08:32:51 +0800, Peter Chen wrote:
> On 21-01-14 13:00:21, Alan Stern wrote:
> > On Thu, Jan 14, 2021 at 01:04:02PM +0800, Peter Chen wrote:
> > > On 21-01-14 11:59:07, Daewoong Kim wrote:
> > > > DMA mapping of urb->setup_packet is not necessary for xHCI host
> > > > controllers. The xHCI specification says that Setup Stage TRB includes
> > > > whole Setup Data; therefore, urb->setup_dma will not be used in the xhci
> > > > HCD code.
> > > > 
> > > 
> > > How about bypass map/unmap operation for xHCI control transfer directly?
> > > 
> > > diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> > > index 91ab81c3fc79..0a0ab14b7638 100644
> > > --- a/drivers/usb/host/xhci.c
> > > +++ b/drivers/usb/host/xhci.c
> > > @@ -1374,7 +1374,8 @@ static int xhci_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
> > > 
> > >  	xhci = hcd_to_xhci(hcd);
> > > 
> > > -	if (xhci_urb_suitable_for_idt(urb))
> > > +	if (xhci_urb_suitable_for_idt(urb) ||
> > > +		(usb_endpoint_xfer_control(&urb->ep->desc)))
> > >  		return 0;
> > 
> > Would this affect the map/unmap operations for the DATA packets in a 
> > control transfer, along with the SETUP packet?
> > 
> 
> Oh, you are right, Alan. We do need map/unmap operation for DATA
> packet in control transfer.

Is it possible to bypass map/unmap operations for MUSB devices' control transfer directly?
If possible, the uses_pio_for_control field in struct usb_bus could be removed.

diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
index ad5a0f405a75..54061764ffda 100644
--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1409,8 +1409,6 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
 	 */
 
 	if (usb_endpoint_xfer_control(&urb->ep->desc)) {
-		if (hcd->self.uses_pio_for_control)
-			return ret;
 		if (hcd->localmem_pool) {
 			ret = hcd_alloc_coherent(
 					urb->dev->bus, mem_flags,
diff --git a/drivers/usb/musb/musb_host.c b/drivers/usb/musb/musb_host.c
index 30c5e7de0761..6eaff08cd1e4 100644
--- a/drivers/usb/musb/musb_host.c
+++ b/drivers/usb/musb/musb_host.c
@@ -2624,6 +2624,8 @@ static int musb_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
 	struct musb	*musb = hcd_to_musb(hcd);
 	int ret;
 
+	if (usb_endpoint_xfer_control(&urb->ep->desc))
+		return 0;
 	/*
 	 * The DMA engine in RTL1.8 and above cannot handle
 	 * DMA addresses that are not aligned to a 4 byte boundary.
@@ -2700,7 +2702,6 @@ int musb_host_alloc(struct musb *musb)
 		return -EINVAL;
 
 	*musb->hcd->hcd_priv = (unsigned long) musb;
-	musb->hcd->self.uses_pio_for_control = 1;
 	musb->hcd->uses_new_polling = 1;
 	musb->hcd->has_tt = 1;
 
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 7d72c4e0713c..f4b7d529f2eb 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -426,10 +426,6 @@ struct usb_bus {
 	struct device *sysdev;		/* as seen from firmware or bus */
 	int busnum;			/* Bus number (in order of reg) */
 	const char *bus_name;		/* stable id (PCI slot_name etc) */
-	u8 uses_pio_for_control;	/*
-					 * Does the host controller use PIO
-					 * for control transfers?
-					 */
 	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? */
--

With Best Regards,
Daewoong Kim