Re: [PATCH v7 2/3] clocksource: Rewrite Xilinx AXI timer driver

[Sean Anderson]

On 9/24/21 2:52 AM, Michal Simek wrote:
> Dear Sean,
>
> On 9/16/21 8:05 PM, Sean Anderson wrote:
> > This rewrites the Xilinx AXI timer driver to be more platform agnostic.
> > Some common code has been split off so it can be reused. These routines
> > currently live in drivers/mfd. The largest changes are summarized below:
> >
> > - We now support any number of timer devices, possibly with only one
> >   counter each. The first counter will be used as a clocksource. Every
> >   other counter will be used as a clockevent. This allocation scheme was
> >   chosen arbitrarily.
> > - We do not use timer_of_init because we need to perform some tasks in
> >   between different stages. For example, we must ensure that ->read and
> >   ->write are initialized before registering the irq. This can only happen
> >   after we have gotten the register base (to detect endianness). We also
> >   have a rather unusual clock initialization sequence in order to remain
> >   backwards compatible. Due to this, it's ok for the initial clock request
> >   to fail, and we do not want other initialization to be undone. Lastly, it
> >   is more convenient to do one allocation for xilinx_clockevent_device than
> >   to do one for timer_of and one for xilinx_timer_priv.
> > - We now pay attention to xlnx,count-width and handle smaller width timers.
> >   The default remains 32.
> > - We access registers using regmap. This automatically deals with
> >   endianness issues, so we no longer have to use our own wrappers. It
> >   also provides locking for clockevents which have to worry about being
> >   interrupted in the middle of a read/modify/write.
> >
> > Note that while the existing timer driver always sets the cpumask to cpu
> > 0, this version sets it to all possible CPUs. I believe this is correct
> > for multiprocessor systems where the timer is not physically wired to a
> > particular CPU's interrupt line. For uniprocessor systems (like most
> > microblaze systems) this makes no difference.
> >
> > Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxx>
> > ---
> > This has been tested on microblaze qemu.
> >
> > Changes in v7:
> > - Add dependency on OF_ADDRESS
> >
> > Changes in v6:
> > - Add __init* attributes
> > - Export common symbols
> > - Fix goto'ing incorrect label for cleanup
> > - Remove duplicate regmap_config
> > - Round to closest period in xilinx_timer_get_period to ensure proper
> >   semantics for xilinx_pwm_get_state
> >
> > Changes in v5:
> > - Fix some overflows when setting the max value for clockevent and
> >   sched_clock
> > - Just use clk_register_fixed_rate instead of the "private" version
> > - Remove duplicate register definitions
> > - Remove xilinx_timer_tlr_period
> > - Remove xlnx,axi-timer-2.0 compatible string
> > - Require that callers check arguments to xilinx_timer_tlr_cycles
> > - Use regmap to deal with endianness issues as suggested by Lee
> >
> > Changes in v4:
> > - Break out clock* drivers into their own file
> >
> >  MAINTAINERS                               |   6 +
> >  arch/microblaze/kernel/Makefile           |   3 +-
> >  arch/microblaze/kernel/timer.c            | 326 ----------------------
> >  drivers/clocksource/Kconfig               |  13 +
> >  drivers/clocksource/Makefile              |   1 +
> >  drivers/clocksource/timer-xilinx-common.c |  71 +++++
> >  drivers/clocksource/timer-xilinx.c        | 323 +++++++++++++++++++++
> >  include/clocksource/timer-xilinx.h        |  91 ++++++
> >  8 files changed, 506 insertions(+), 328 deletions(-)
> >  delete mode 100644 arch/microblaze/kernel/timer.c
> >  create mode 100644 drivers/clocksource/timer-xilinx-common.c
> >  create mode 100644 drivers/clocksource/timer-xilinx.c
> >  create mode 100644 include/clocksource/timer-xilinx.h
>
>
> I have said it couple of times. I won't accept this in this form.
> I have no problem to move this driver out of microblaze. But I want to
> see transition from current state to new state and check it with baby
> steps which are bisectable if any problem happens.
> Because in this style we end in this patch and it will take some time to
> find out what it is failing.

Unfortunately, I do not have the time do do this at the moment. Because
these drivers are independent in nature, I propose to drop these changes
to the timer driver, but leave the common functions split out. In the
future, I (or you) may come back and make the changes in this patch in
an incremental fashion. The only change necessary for this driver would
be to check for #pwm-cells.

--Sean