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

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Date:   Thu, 5 Nov 2020 11:04:54 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jiri Slaby' <jirislaby@...nel.org>,
        Lee Jones <lee.jones@...aro.org>
CC:     "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

> >> 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...

	David

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