Re: Regression: bd698d24b1b57: i2c: designware: Get selected speed mode sda-hold-time via ACPI

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

[+ Ken, Jeff]

On Tue, May 09, 2017 at 05:54:11PM +0300, Andy Shevchenko wrote:
> On Tue, 2017-05-09 at 15:07 +0100, Lorenzo Pieralisi wrote:
> > Hi guys,
> > 
> > as a heads-up, with today mainline (commit 2868b2513aa7) I get the
> > following splat on AMD Seattle, reverting the $SUBJECT commit "solves"
> > the problem.
> > 
> > My I2C knowledge is a bit limited but I am not sure I understand why
> > we should be reading eg ss_hcnt/ss_lcnt depending on the dev->clk_freq
> > but then i2c_dw_init() _always_ requires those values to be set for
> > a given device. Again, I have no insights into I2C inner workings
> > so apologies for the silly assumption/question.
> > 
> > Please have a look into this, thanks.
> 
> Since there is no clock defined you got a warning.

IIUC there has never been a clock defined for this platform, that's
the problem. The warning appeared because the commit in $SUBJECT
prevents reading the ss_hcnt and ss_lcnt values from ACPI methods
that are there in ACPI tables (SSCN and FMCN), because it carries
out the SSCN FMCN look-up depending on the dev->clk_freq value.

Before $SUBJECT commit the values were read unconditionally from SSCN
and FMCN ACPI methods IIUC, again, I am no I2C expert so it is more
a question than anything else.

dev->clk_freq is set to 400000 by default because FW does not the
contain (ie never contained) "clock-frequency" property and
acpi_speed can't be ascertained through I2C resources, that's how
I read what's happening.

> It means either ID is not added to drivers/acpi/acpi_apd.c or
> platform has wrong values and thus 
> dw_i2c_no_acpi_params should be expanded.
> 
> I have no such platform, so I can't tell which one is the right fix.
> But it's not a revert by my opinion.

It was working before the commit in $SUBJECT was applied, AMD chaps
may be able to chime in hopefully to clarify, whether that's a revert
or not we shall see but with a given FW the kernel behaviour changed,
it may affect other platforms too if their FW was not upgraded
accordingly that's why I reported it.

Thanks !
Lorenzo

> 
> > [    1.160597] ------------[ cut here ]------------
> > [    1.165207] WARNING: CPU: 0 PID: 1 at drivers/i2c/busses/i2c-
> > designware-core.c:293 i2c_dw_clk_rate+0x20/0x30
> > 
> 
> -- 
> Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Intel Finland Oy