Re: [BISECTED] OMAP: DSS: clk rate mismatch

[Tero Kristo]

On 01/28/2014 11:48 AM, Tomi Valkeinen wrote:
> On 2014-01-28 11:35, Christoph Fritz wrote:
> > On Tue, 2014-01-28 at 11:04 +0200, Tomi Valkeinen wrote:
> > > On 2014-01-27 20:41, Christoph Fritz wrote:
> > > > On Mon, 2014-01-27 at 19:30 +0200, Ivaylo Dimitrov wrote:
> > > > > linux-next-20140124 DSS is broken on N900  - display stays black (there
> > > > > is some noise though). I booted the kernel with qemu and it gives the
> > > > > following warning:
> > > > >
> > > > > [    0.623779] DSS: set fck to 172800000
> > > > > [    0.624237] ------------[ cut here ]------------
> > > > > [    0.624298] WARNING: CPU: 0 PID: 1 at
> > > > > drivers/video/omap2/dss/dss.c:497 dss_set_fck_rate+0x68/0x8c()
> > > > > [    0.624359] clk rate mismatch: 288000000 != 172800000
> > > >
> > > > Here are also clock regressions since next-20140122 regarding
> > > > dss_set_fck_rate() and sys_clkout2 occuring in my current patchset for a
> > > > dm37xx100 board. Please see here:
> > >
> > > I presume you get a similar warning on your board? What rates does it
> > > report?
> >
> > None, dss_set_fck_rate() just fails so omapdss_dss exits with error -22.
>
> Ok, then it's something else. That means clk_set_rate() fails.
>
> If you can do some tests, you could print the rate that the
> dss_set_fck_rate() is given, to see that it's something reasonable, and
> also do a clk_get_rate(dss.dss_clk) to see that the clock itself is ok
> and there's some valid rate there.
>
> > To quote the cover-letter[1] of my board-support patch series here:
> >
> > Due to a regression since next-20140122 the following errors are present:
> >
> >   - pin sys_clkout2, which gets configured to 24 Mhz by the fourth patch
> >     in this set, erroneously outputs only 12 Mhz.
> >     Just out of curiosity, configuring it to 48 Mhz puts out desired 24 Mhz.
> >
> >   - omap_dss, which gets configured by the third patch in this set, fails
> >     to do 'dss_set_fck_rate(fck);' in
> >     drivers/video/omap2/dss/dss.c:dss_setup_default_clock() which leads to:
> >
> >      | omapdss_dss: probe of omapdss_dss failed with error -22
> >      | omapdss CORE error: Failed to initialize DSS platform driver
> >      | panel-dpi panel-dpi.0: failed to find video source 'dpi.0
> >
> >    Both regressions seem to have something to do with the clock framework.
> >    Could this be related to the DT clock conversion patches?
>
> No idea...

Yea its definitely possible, as the clock DT conversion touches pretty 
much everything. Have you tried whether this works properly with legacy 
boot? Personally I don't have access to any omap3 devices that would 
have display and have no possibility to check this out myself. Anyway, 
my initial guess is that some clock divider setup might be wrong with 
omap3, or we are missing some ti,set-rate-parent flag for some clock 
node which prevents escalating clk_set_rate properly. However, it should 
be easy to debug this by looking at the clock node in question, and its 
parent nodes to see if there are any problems.

-Tero
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