Re: [PATCH v10 3/3] pwm: Add support for Xilinx AXI Timer

From: Michal Simek
Date: Thu Nov 18 2021 - 03:36:12 EST

On 11/17/21 17:23, Thierry Reding wrote:
On Fri, Nov 12, 2021 at 01:55:04PM -0500, Sean Anderson wrote:
This adds PWM support for Xilinx LogiCORE IP AXI soft timers commonly
found on Xilinx FPGAs. At the moment clock control is very basic: we
just enable the clock during probe and pin the frequency. In the future,
someone could add support for disabling the clock when not in use.

Some common code has been specially demarcated. While currently only
used by the PWM driver, it is anticipated that it may be split off in
the future to be used by the timer driver as well.

This driver was written with reference to Xilinx DS764 for v1.03.a [1].


Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxx>

Changes in v10:
- Fix compilation error in timer driver

Changes in v9:
- Refactor "if { return } else if { }" to "if { return } if { }"
- Remove drivers/clocksource/timer-xilinx-common.c from MAINTAINERS
- Remove xilinx_timer_common_init and integrate it into xilinx_timer_probe

Changes in v8:
- Drop new timer driver; it has been deferred for future series

Changes in v7:
- Add dependency on OF_ADDRESS
- Fix period_cycles calculation
- Fix typo in limitations

Changes in v6:
- Capitalize error messages
- Don't disable regmap locking to allow inspection of registers via
- Prevent overflow when calculating period_cycles
- Remove enabled variable from xilinx_pwm_apply
- Swap order of period_cycle range comparisons

Changes in v5:
- Allow non-zero #pwm-cells
- Correctly set duty_cycle in get_state when TLR0=TLR1
- Elaborate on limitation section
- Perform some additional checks/rounding in apply_state
- Remove xlnx,axi-timer-2.0 compatible string
- Rework duty-cycle and period calculations with feedback from Uwe
- Switch to regmap to abstract endianness issues
- Use more verbose error messages

Changes in v4:
- Don't use volatile in read/write replacements. Some arches have it and
some don't.
- Put common timer properties into their own struct to better reuse
- Remove references to properties which are not good enough for Linux.

Changes in v3:
- Add clockevent and clocksource support
- Remove old microblaze driver
- Rewrite probe to only use a device_node, since timers may need to be
initialized before we have proper devices. This does bloat the code a bit
since we can no longer rely on helpers such as dev_err_probe. We also
cannot rely on device resources being free'd on failure, so we must free
them manually.
- We now access registers through xilinx_timer_(read|write). This allows us
to deal with endianness issues, as originally seen in the microblaze
driver. CAVEAT EMPTOR: I have not tested this on big-endian!

Changes in v2:
- Add comment describing device
- Add comment explaining why we depend on !MICROBLAZE
- Add dependencies on COMMON_CLK and HAS_IOMEM
- Cast dividends to u64 to avoid overflow
- Check for over- and underflow when calculating TLR
- Check range of xlnx,count-width
- Don't compile this module by default for arm64
- Don't set pwmchip.base to -1
- Ensure the clock is always running when the pwm is registered
- Remove debugfs file :l
- Report errors with dev_error_probe
- Set xilinx_pwm_ops.owner
- Use NSEC_TO_SEC instead of defining our own
- Use TCSR_RUN_MASK to check if the PWM is enabled, as suggested by Uwe

arch/microblaze/kernel/timer.c | 3 +


do you mind giving an Acked-by for this part. It looks harmless enough,
but just making sure you're aware of this.

That's fine for me.

Acked-by: Michal Simek <michal.simek@xxxxxxxxxx>