linux-kernel - Re: [PATCH] USB: ehci-pci: USB host controller support for Intel Quark X1000

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Date:	Tue, 24 Jun 2014 09:24:44 -0400
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	"Chen, Alvin" <alvin.chen@...el.com>
Cc:	Alan Stern <stern@...land.harvard.edu>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Boon Leong Ong <boon.leong.ong@...el.com>
Subject: Re: [PATCH] USB: ehci-pci: USB host controller support for Intel
 Quark X1000

On Tue, Jun 24, 2014 at 08:51:43AM -0700, Chen, Alvin wrote:
> From: Bryan O'Donoghue <bryan.odonoghue@...el.com>
> 
> This patch is to enable USB host controller for Intel Quark X1000. Add pci quirks
> to adjust the packet buffer in/out threshold value, and ensure EHCI packet buffer
> i/o threshold value is reconfigured to half.
> 
> Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@...el.com>
> Signed-off-by: Alvin (Weike) Chen <alvin.chen@...el.com>
> ---
>  drivers/usb/host/ehci-pci.c   |    4 ++++
>  drivers/usb/host/pci-quirks.c |   42 +++++++++++++++++++++++++++++++++++++++++
>  drivers/usb/host/pci-quirks.h |    2 ++
>  3 files changed, 48 insertions(+)
> 
> diff --git a/drivers/usb/host/ehci-pci.c b/drivers/usb/host/ehci-pci.c
> index 3e86bf4..33cfa23 100644
> --- a/drivers/usb/host/ehci-pci.c
> +++ b/drivers/usb/host/ehci-pci.c
> @@ -50,6 +50,10 @@ static int ehci_pci_reinit(struct ehci_hcd *ehci, struct pci_dev *pdev)
>  	if (!retval)
>  		ehci_dbg(ehci, "MWI active\n");
>  
> +	/* Reset the threshold limit */
> +	if(unlikely(usb_is_intel_qrk(pdev)))

Why unlikely()?  Have you measured a speed difference here?  And this is
a _very_ slow path, what does that speed difference you measured help
with?

thanks,

greg k-h
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