[linux-sunxi] Re: [PATCH v2 1/3] reset: Add shared reset_control_[de]assert variants

On 4 January 2016 at 21:39, Philipp Zabel [off-list ref] wrote:

Am Samstag, den 19.12.2015, 11:55 +0100 schrieb Hans de Goede:

quoted

On 18-12-15 12:08, Maxime Ripard wrote:

quoted

quoted

     - If the reset line is in a !exclusive use with more than 1 user,
       the refcount is modified and an error is returned to notify that
       it didn't happen.

Also ack, except for returning the error, if a driver has used
reset_control_get_shared, it should simply be aware that doing an assert
might not necessarily actually assert the line, just like doing a clk-disable
does not really necessary disable the clock, etc. If a driver is not prepared
to deal with this, it should simply not use reset_control_get_shared.

I see returning an error if the assert did not happen due to other users /
deassert_count != 0 as inconsistent compared to how clks, regulators and phys
handle this, these all simply return success in this case.

I wouldn't want drivers to have to differentiate between relevant and
irrelevant error codes, so in the clock-like refcounting use case
reset_assert should not return an error if it just correctly decremented
the refcount. I'd still prefer to have separate API for the counted
must_deassert/may_assert vs the exclusive must_assert/must_deassert use
cases, but I just can't think of a good name.

Maybe something along the lines of assert_now or assert_sync. It
should be possible to call on shared line and then get an error when
the operation is blocked by other user.

The driver may not really care. Depending on the hardware the line can
be shared on one device and exclusive on another. The driver may just
let the line go when the device is powered off. And it may require a
reset cycle when it detects the device is hosed and return an error
when the reset fails for whatever reason.

Thanks

Michal