Re: [PATCH 2/9] crypto: atmel-ecc: Silently ignore missing clock frequency

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On Mon, Jun 11, 2018 at 11:46 AM Tudor Ambarus
<tudor.ambarus@xxxxxxxxxxxxx> wrote:
> On 06/05/2018 04:49 PM, Linus Walleij wrote:
> > The Atmel ECC driver contains a check for the I2C bus clock
> > frequency, so as to check that the I2C adapter in use
> > satisfies the device specs.
> >
> > If the device is connected to a device tree node that does not
> > contain a clock frequency setting, such as an I2C mux or gate,
> > this blocks the probe. Make the probe continue silently if
> > no clock frequency can be found, assuming all is safe.
>
> I don't think it's safe. We use bus_clk_rate to compute the ecc508's
> wake token. If you can't wake the device, it will ignore all your
> commands.

I see. I wonder why it works so well for me then?
Could we just print a warning and continue?
The general advice for the kernel is not to bail out if
hardware is not optimally configured, but continue with
a warning that maybe not everything is all right.

> My proposal was to introduce a bus_freq_hz member in the i2c_adapter
> structure (https://patchwork.kernel.org/patch/10307637/), but I haven't
> received feedback yet, Wolfram?
>
> I would say first to check the bus_freq_hz from adapter (if it will be
> accepted) else to look into dt and, in the last case, if nowhere
> provided, to block the probe.

So blocking the probe because we are not 100% sure the hardware
will work is against established practice: the established practice
is to be liberal with letting probe() continue, but emit a warning.

In my case that is good because it makes the hardware probe
and work without any visible problems.

I *can* try to traverse the device tree upwards from the mux node
to find the parent I2C controller and its "clock-frequency"
property. I felt that was hackish, but if you prefer the hack I
can try to use that.

Yours,
Linus Walleij



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