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SubjectRe: [PATCH v5 09/23] drm/i2c: tda998x: don't read write-only registers
On Sun, Feb 02, 2014 at 06:45:12PM +0100, Jean-Francois Moine wrote:
> On Sun, 2 Feb 2014 16:23:09 +0000
> Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:
>
> > On Sat, Jan 25, 2014 at 06:14:42PM +0100, Jean-Francois Moine wrote:
> > > This patch takes care of the write-only registers of the tda998x.
> > >
> > > The registers SOFTRESET, TBG_CNTRL_0 and TBG_CNTRL_1 have all bits
> > > cleared after reset, so, they may be fully re-written.
> > >
> > > The register MAT_CONTRL is set to
> > > MAT_CONTRL_MAT_BP | MAT_CONTRL_MAT_SC(1)
> > > after reset, so, it may be fully set again to this value.
> >
> > I said in v3 of this patch, which seems to remain unaddressed:
> >
> > > /* must be last register set: */
> > > - reg_clear(priv, REG_TBG_CNTRL_0, TBG_CNTRL_0_SYNC_ONCE);
> > > + reg_write(priv, REG_TBG_CNTRL_0, 0);
> >
> > Register changes which have a potential effect shouldn't be part of a
> > patch which is really only trying to avoid reading from write only
> > registers.
> >
> > This could be a potential functional change - and it's probably one
> > which Rob Clark should at least be made aware of. As I commented last
> > time, when you're changing register values in an otherwise innocuous
> > patch, you should comment about them in the patch description.
>
> According to the tda9983b documentation, the register TBG_CNTRL_0 is
> set to 0 at reset time. I think that it is the same for all the tda998x
> family. In the other hand, this register is supposed to be write only,
> so reading it may return any value, and the reg_clear() function may
> set any other bits. Then, clearing one bit is less secure than clearing
> the full register.

Okay, in that case I'm happy with this patch.

--
FTTC broadband for 0.8mile line: 5.8Mbps down 500kbps up. Estimation
in database were 13.1 to 19Mbit for a good line, about 7.5+ for a bad.
Estimate before purchase was "up to 13.2Mbit".


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