linux-kernel - Re: [PATCH 11/30] usb: dwc2: gadget: Avoid pointless read of EP control register

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Message-ID: <20200704060446.GA20254@kroah.com>
Date:   Sat, 4 Jul 2020 08:04:46 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Minas Harutyunyan <Minas.Harutyunyan@...opsys.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Ben Dooks <ben@...tec.co.uk>
Subject: Re: [PATCH 11/30] usb: dwc2: gadget: Avoid pointless read of EP
 control register

On Fri, Jul 03, 2020 at 06:16:26PM +0100, Lee Jones wrote:
> On Fri, 03 Jul 2020, Minas Harutyunyan wrote:
> 
> > Hi,
> > 
> > On 7/3/2020 11:29 AM, Greg KH wrote:
> > > On Thu, Jul 02, 2020 at 03:46:06PM +0100, Lee Jones wrote:
> > >> Commit ec1f9d9f01384 ("usb: dwc2: gadget: parity fix in isochronous mode") moved
> > >> these checks to dwc2_hsotg_change_ep_iso_parity() back in 2015.  The assigned
> > >> value hasn't been read back since.  Let's remove the unnecessary H/W read.
> > >>
> > >> Fixes the following W=1 warning:
> > >>
> > >>   drivers/usb/dwc2/gadget.c: In function ‘dwc2_hsotg_epint’:
> > >>   drivers/usb/dwc2/gadget.c:2981:6: warning: variable ‘ctrl’ set but not used [-Wunused-but-set-variable]
> > >>   2981 | u32 ctrl;
> > >>   | ^~~~
> > >>
> > >> Cc: Minas Harutyunyan <hminas@...opsys.com>
> > >> Cc: Ben Dooks <ben@...tec.co.uk>
> > >> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> > >> ---
> > >>   drivers/usb/dwc2/gadget.c | 2 --
> > >>   1 file changed, 2 deletions(-)
> > >>
> > >> diff --git a/drivers/usb/dwc2/gadget.c b/drivers/usb/dwc2/gadget.c
> > >> index 116e6175c7a48..fa07e3fcb8841 100644
> > >> --- a/drivers/usb/dwc2/gadget.c
> > >> +++ b/drivers/usb/dwc2/gadget.c
> > >> @@ -2975,10 +2975,8 @@ static void dwc2_hsotg_epint(struct dwc2_hsotg *hsotg, unsigned int idx,
> > >>   	u32 epctl_reg = dir_in ? DIEPCTL(idx) : DOEPCTL(idx);
> > >>   	u32 epsiz_reg = dir_in ? DIEPTSIZ(idx) : DOEPTSIZ(idx);
> > >>   	u32 ints;
> > >> -	u32 ctrl;
> > >>   
> > >>   	ints = dwc2_gadget_read_ep_interrupts(hsotg, idx, dir_in);
> > >> -	ctrl = dwc2_readl(hsotg, epctl_reg);
> > > 
> > > As you know, lots of hardware requires reads to happen to do things, so
> > > are you sure it is safe to remove this read call?
> > > 
> > 
> > Greg, yes, it's Ok to remove this unnecessary read which remained from 
> > previous implementations.
> > 
> > Lee, please add "Fixes:" tag and resubmit v2.
> 
> Is this suitable for Stable Greg?

Does it fix something that people have ever noticed or care about?
Given the age of the bug, I doubt it :)

thanks,

greg k-h