linux-kernel - Re: [PATCH 2/6] ALSA: line6: Add delay before reading status

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Date:	Wed, 11 Feb 2015 10:34:05 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Chris Rorvick <chris@...vick.com>
Cc:	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
	Stefan Hajnoczi <stefanha@...il.com>
Subject: Re: [PATCH 2/6] ALSA: line6: Add delay before reading status

At Tue, 10 Feb 2015 23:03:13 -0600,
Chris Rorvick wrote:
> 
> The device indicates the result of a read/write operation by making the
> status available on a subsequent request from the driver.  This is not
> ready immediately, though, so the driver is currently slamming the
> device with hundreds of pointless requests before getting the expected
> response.  Add a two millisecond delay before each attempt.  This is
> approximately the behavior observed with version 4.2.7.1 of the Windows
> driver.
> 
> Signed-off-by: Chris Rorvick <chris@...vick.com>

Applied, thanks.


Takashi

> ---
>  sound/usb/line6/driver.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/sound/usb/line6/driver.c b/sound/usb/line6/driver.c
> index aac1e35..222c14f 100644
> --- a/sound/usb/line6/driver.c
> +++ b/sound/usb/line6/driver.c
> @@ -296,6 +296,8 @@ static void line6_data_received(struct urb *urb)
>  	line6_start_listen(line6);
>  }
>  
> +#define LINE6_READ_WRITE_STATUS_DELAY 2  /* milliseconds */
> +
>  /*
>  	Read data from device.
>  */
> @@ -319,6 +321,8 @@ int line6_read_data(struct usb_line6 *line6, u16 address, void *data,
>  
>  	/* Wait for data length. We'll get 0xff until length arrives. */
>  	do {
> +		mdelay(LINE6_READ_WRITE_STATUS_DELAY);
> +
>  		ret = usb_control_msg(usbdev, usb_rcvctrlpipe(usbdev, 0), 0x67,
>  				      USB_TYPE_VENDOR | USB_RECIP_DEVICE |
>  				      USB_DIR_IN,
> @@ -376,6 +380,8 @@ int line6_write_data(struct usb_line6 *line6, u16 address, void *data,
>  	}
>  
>  	do {
> +		mdelay(LINE6_READ_WRITE_STATUS_DELAY);
> +
>  		ret = usb_control_msg(usbdev, usb_rcvctrlpipe(usbdev, 0),
>  				      0x67,
>  				      USB_TYPE_VENDOR | USB_RECIP_DEVICE |
> -- 
> 2.1.0
> 
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