linux-kernel - Re: [PATCH RFC] usb: dwc2: host: use msleep() for long delay

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Date:   Thu, 12 Jan 2017 16:35:06 -0800
From:   John Youn <John.Youn@...opsys.com>
To:     Nicholas Mc Guire <hofrat@...dl.org>,
        John Youn <John.Youn@...opsys.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] usb: dwc2: host: use msleep() for long delay

On 1/12/2017 7:15 AM, Nicholas Mc Guire wrote:
> ulseep_range() uses hrtimers and provides no advantage over msleep()
> for larger delays. Fix up the 100ms delays here passing the adjusted "min"
> value to msleep(). This helps reduce the load on the hrtimer subsystem.
> 
> Link: https://urldefense.proofpoint.com/v2/url?u=http-3A__lkml.org_lkml_2017_1_11_377&d=DgIBAg&c=DPL6_X_6JkXFx7AXWqB0tg&r=U3o8uKoKhWme5_V9D-eeCkB11BFwt4KvWztBgdE9ZpA&m=dvQDbbH_QF2kZjARIDPimFAK95z8eOnw04feJuHCrJg&s=Prc0m1oUG4u8n8TFK-fdgzitMzE2ep6pM3L6y_DQeRs&e= 
> Fixes: commit 2938fc63e0c2 ("usb: dwc2: Properly account for the force mode delays")
> Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> ---
> Problem was found by cocinelle script.
> 
> Note that this originally was an msleep(25) then commit 2938fc63e0c2 
> ("usb: dwc2: Properly account for the force mode delays") changed this 
> to usleep_range(100000,110000) with the comment in the function head:
> <snip>
>  After clearing the bits, wait up to 100 ms to account for any
>  potential IDDIG filter delay...
> <snip>
> but without explaining why the API was switched to usleep_range() here
> It does not look like there is any reason for using a high resolution 
> timer here - the stated requirement is clearly satisfied by msleep(100)
> as well. But it originally was usleep_range(150000, 160000) in
> commit 09c96980dc72 ("usb: dwc2: Add functions to set and clear force mode")
> so not sure if I am not overlooking some reason for the highrestimer here ?
> 
> This needs to be clarified by someone that knows the details and history
> of this device/driver.
> 
> Patch was compile tested with: x86_64_defconfig + CONFIG_USB_DWC2
> 
> Patch is aginast 4.10-rc3 (localversion-next is next-20170112)
> 
>  drivers/usb/dwc2/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/dwc2/core.c b/drivers/usb/dwc2/core.c
> index 11d8ae9..439a21b 100644
> --- a/drivers/usb/dwc2/core.c
> +++ b/drivers/usb/dwc2/core.c
> @@ -455,7 +455,7 @@ void dwc2_clear_force_mode(struct dwc2_hsotg *hsotg)
>  	dwc2_writel(gusbcfg, hsotg->regs + GUSBCFG);
>  
>  	if (dwc2_iddig_filter_enabled(hsotg))
> -		usleep_range(100000, 110000);
> +		msleep(100);
>  }
>  
>  /*
> 

+Felipe

Acked-by: John Youn <johnyoun@...opsys.com>

John