Re: [RFC PATCH 2/2] usb: storage: scsiglue: limit USB3 devices to 2048 sectors

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On Wed, Nov 04, 2015 at 02:48:32PM -0600, Felipe Balbi wrote:
> USB3 devices, because they are much newer, have much
> less chance of having issues with larger transfers.
> 
> We still keep a limit because anything above 2048
> sectors really rendered negligible speed
> improvements, so we will simply ignore
> that. Transferring 1MiB should already give us
> pretty good performance.
> 
> Signed-off-by: Felipe Balbi <balbi@xxxxxx>
> ---
>  drivers/usb/storage/scsiglue.c | 16 +++++++++++-----
>  drivers/usb/storage/usb.c      |  4 ++++
>  include/linux/usb_usual.h      |  2 ++
>  3 files changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/usb/storage/scsiglue.c b/drivers/usb/storage/scsiglue.c
> index 00aadf3a3857..bda2b3c9ae42 100644
> --- a/drivers/usb/storage/scsiglue.c
> +++ b/drivers/usb/storage/scsiglue.c
> @@ -115,13 +115,19 @@ static int slave_configure(struct scsi_device *sdev)
>  {
>  	struct us_data *us = host_to_us(sdev->host);
>  
> -	/* Many devices have trouble transferring more than 32KB at a time,
> -	 * while others have trouble with more than 64K. At this time we
> -	 * are limiting both to 32K (64 sectores).
> -	 */
> -	if (us->fflags & (US_FL_MAX_SECTORS_64 | US_FL_MAX_SECTORS_MIN)) {
> +	if (us->fflags & US_FL_USB3) {
> +		/* USB3 devices will be limitted at 2048 sectors. This gives us

"limited"?

Other than that, this looks good to me, did you have a chance to test a
Windows machine to see what it does?

thanks,

greg k-h
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