From: Felipe Balbi <felipe.balbi@linux.intel.com> To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>, oneukum@suse.com, Mathias Nyman <mathias.nyman@intel.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC v2] usb: xhci: add Immediate Data Transfer support Date: Wed, 06 Feb 2019 12:54:50 +0200 [thread overview] Message-ID: <871s4lmbk5.fsf@linux.intel.com> (raw) In-Reply-To: <294f2492f8d3b7022bf659dcb473c45a34e85db8.camel@suse.de> [-- Attachment #1: Type: text/plain, Size: 2148 bytes --] Hi, Nicolas Saenz Julienne <nsaenzjulienne@suse.de> writes: >> > diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c >> > index 005e65922608..dec62f7f5dc8 100644 >> > --- a/drivers/usb/host/xhci.c >> > +++ b/drivers/usb/host/xhci.c >> > @@ -1238,6 +1238,21 @@ EXPORT_SYMBOL_GPL(xhci_resume); >> > >> > /*------------------------------------------------------------------------- >> > */ >> > >> > +/* >> > + * Bypass the DMA mapping if URB is suitable for Immediate Transfer (IDT), >> > + * we'll copy the actual data into the TRB address register. This is >> > limited to >> > + * transfers up to 8 bytes on output endpoints of any kind with >> > wMaxPacketSize >> > + * >= 8 bytes. >> > + */ >> > +static int xhci_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb, >> > + gfp_t mem_flags) >> > +{ >> > + if (xhci_urb_suitable_for_idt(urb)) >> > + return 0; >> > + >> > + return usb_hcd_map_urb_for_dma(hcd, urb, mem_flags); >> > +} >> >> don't you need a matching unmap_urb_for_dma()?? > > Not really as every DMA mapping sets a matching URB flag to track it. For > example when usb_hcd_map_urb_for_dma() uses dma_map_single() it will set > URB_DMA_MAP_SINGLE in urb->transfer_flags, later on unmap_urb_for_dma() will > catch it and unmap it. As I bypass the mapping altogether there are no > flags set, so unmap_urb_for_dma() won't have any effect. > > I could still add it for clarity, and well, I guess it'll save some > instructions on the IDT suitable side. thanks for the clarification. >> > diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h >> > index 652dc36e3012..9d77b0901ab7 100644 >> > --- a/drivers/usb/host/xhci.h >> > +++ b/drivers/usb/host/xhci.h >> > @@ -1295,6 +1295,8 @@ enum xhci_setup_dev { >> > #define TRB_IOC (1<<5) >> > /* The buffer pointer contains immediate data */ >> > #define TRB_IDT (1<<6) >> > +/* TDs smaller than this might use IDT */ >> >> Technically, "TDs at most this" since you're 8 itself is an allowed heh, I made a mess on this sentence, but I guess you got the gist of it. cheers -- balbi [-- Attachment #2: signature.asc --] [-- Type: application/pgp-signature, Size: 832 bytes --]
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From: Felipe Balbi <felipe.balbi@linux.intel.com> To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>, oneukum@suse.com, Mathias Nyman <mathias.nyman@intel.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [RFC,v2] usb: xhci: add Immediate Data Transfer support Date: Wed, 06 Feb 2019 12:54:50 +0200 [thread overview] Message-ID: <871s4lmbk5.fsf@linux.intel.com> (raw) Hi, Nicolas Saenz Julienne <nsaenzjulienne@suse.de> writes: >> > diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c >> > index 005e65922608..dec62f7f5dc8 100644 >> > --- a/drivers/usb/host/xhci.c >> > +++ b/drivers/usb/host/xhci.c >> > @@ -1238,6 +1238,21 @@ EXPORT_SYMBOL_GPL(xhci_resume); >> > >> > /*------------------------------------------------------------------------- >> > */ >> > >> > +/* >> > + * Bypass the DMA mapping if URB is suitable for Immediate Transfer (IDT), >> > + * we'll copy the actual data into the TRB address register. This is >> > limited to >> > + * transfers up to 8 bytes on output endpoints of any kind with >> > wMaxPacketSize >> > + * >= 8 bytes. >> > + */ >> > +static int xhci_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb, >> > + gfp_t mem_flags) >> > +{ >> > + if (xhci_urb_suitable_for_idt(urb)) >> > + return 0; >> > + >> > + return usb_hcd_map_urb_for_dma(hcd, urb, mem_flags); >> > +} >> >> don't you need a matching unmap_urb_for_dma()?? > > Not really as every DMA mapping sets a matching URB flag to track it. For > example when usb_hcd_map_urb_for_dma() uses dma_map_single() it will set > URB_DMA_MAP_SINGLE in urb->transfer_flags, later on unmap_urb_for_dma() will > catch it and unmap it. As I bypass the mapping altogether there are no > flags set, so unmap_urb_for_dma() won't have any effect. > > I could still add it for clarity, and well, I guess it'll save some > instructions on the IDT suitable side. thanks for the clarification. >> > diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h >> > index 652dc36e3012..9d77b0901ab7 100644 >> > --- a/drivers/usb/host/xhci.h >> > +++ b/drivers/usb/host/xhci.h >> > @@ -1295,6 +1295,8 @@ enum xhci_setup_dev { >> > #define TRB_IOC (1<<5) >> > /* The buffer pointer contains immediate data */ >> > #define TRB_IDT (1<<6) >> > +/* TDs smaller than this might use IDT */ >> >> Technically, "TDs at most this" since you're 8 itself is an allowed heh, I made a mess on this sentence, but I guess you got the gist of it. cheers
next prev parent reply other threads:[~2019-02-06 10:54 UTC|newest] Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-02-05 19:56 [RFC v2] usb: xhci: add Immediate Data Transfer support Nicolas Saenz Julienne 2019-02-05 19:56 ` [RFC,v2] " Nicolas Saenz Julienne 2019-02-06 6:35 ` [RFC v2] " Felipe Balbi 2019-02-06 6:35 ` [RFC,v2] " Felipe Balbi 2019-02-06 10:08 ` [RFC v2] " Nicolas Saenz Julienne 2019-02-06 10:08 ` [RFC,v2] " Nicolas Saenz Julienne 2019-02-06 10:54 ` Felipe Balbi [this message] 2019-02-06 10:54 ` Felipe Balbi
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