linux-kernel - Re: [RFC v2] usb: xhci: add Immediate Data Transfer support

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Message-ID: <87lg2tmnk3.fsf@linux.intel.com>
Date:   Wed, 06 Feb 2019 08:35:40 +0200
From:   Felipe Balbi <felipe.balbi@...ux.intel.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>, oneukum@...e.com,
        Mathias Nyman <mathias.nyman@...el.com>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC v2] usb: xhci: add Immediate Data Transfer support


Hi,

Nicolas Saenz Julienne <nsaenzjulienne@...e.de> writes:
> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> index 40fa25c4d041..a4efbe62a1a3 100644
> --- a/drivers/usb/host/xhci-ring.c
> +++ b/drivers/usb/host/xhci-ring.c
> @@ -3272,8 +3272,15 @@ int xhci_queue_bulk_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
>  			field |= TRB_IOC;
>  			more_trbs_coming = false;
>  			td->last_trb = ring->enqueue;
> +
> +			if (xhci_urb_suitable_for_idt(urb)) {
> +				memcpy(&send_addr, urb->transfer_buffer,
> +				       trb_buff_len);
> +				field |= TRB_IDT;
> +			}
>  		}
>  
> +

trailing change

> @@ -3411,6 +3418,12 @@ int xhci_queue_ctrl_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
>  	if (urb->transfer_buffer_length > 0) {
>  		u32 length_field, remainder;
>  
> +		if (xhci_urb_suitable_for_idt(urb)) {
> +			memcpy(&urb->transfer_dma, urb->transfer_buffer,
> +			       urb->transfer_buffer_length);
> +			field |= TRB_IDT;
> +		}
> +
>  		remainder = xhci_td_remainder(xhci, 0,
>  				urb->transfer_buffer_length,
>  				urb->transfer_buffer_length,
> @@ -3420,6 +3433,7 @@ int xhci_queue_ctrl_tx(struct xhci_hcd *xhci, gfp_t mem_flags,
>  				TRB_INTR_TARGET(0);
>  		if (setup->bRequestType & USB_DIR_IN)
>  			field |= TRB_DIR_IN;
> +

trailing change

> 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()??

> 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
size.

-- 
balbi

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