linux-kernel - Re: [PATCH 27/36] tty: synclinkmp: Mark never checked 'readval' as __always

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Date:   Thu, 5 Nov 2020 11:27:28 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Jiri Slaby' <jirislaby@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "paulkf@...rogate.com" <paulkf@...rogate.com>
Subject: Re: [PATCH 27/36] tty: synclinkmp: Mark never checked 'readval' as
 __always_unused

On Thu, 05 Nov 2020, David Laight wrote:

> > >> And the loop can be turned into ndelay:
> > >>
> > >>          /*
> > >>           * Force at least 170ns delay before clearing
> > >>           * reset bit. Each read from LCR takes at least
> > >>           * 30ns so 10 times for 300ns to be safe.
> > >>           */
> > >>          for(i=0;i<10;i++)
> > >>                  readval = *MiscCtrl;
> > >
> > > Again, since I can't test this, I do not want this patch to contain
> > > any functional changes.  AFAIC, the 10 register reads must still
> > > happen after this patch is applied.
> 
> You can't use ndelay(); the writes can get posted so can appear
> much closer together by the time they get to the actual hardware.
> Multiple volatile reads don't need a target variable.
> (Shouldn't they also real readl()?)
> 
> Deleting the driver works...

Will post the removal patches when my tests finish.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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