[PATCH v14 2/2] pwm: Add support for Xilinx AXI Timer

[Thierry Reding]

On Thu, Mar 03, 2022 at 05:35:43PM -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].
> 
> [1] https://www.xilinx.com/support/documentation/ip_documentation/axi_timer/v1_03_a/axi_timer_ds764.pdf
> 
> Signed-off-by: Sean Anderson <sean.anderson at seco.com>
> Acked-by: Michal Simek <michal.simek at xilinx.com>
> ---
> 
> Changes in v14:
> - 1GHz -> 1 GHz
> - Clarify that we will give a very wrong estimate for rate >= 1 GHz
> - Remove duplicate blank line
> - Remove forward declaration of xilinx_timer_common_init (which no
>   longer exists).
> 
> Changes in v13:
> - Clamp period/duty_cycle by assuming rate is at most U32_MAX
> - Expand comment in xilinx_timer_get_period
> - Note that the 100% duty cycle calculations may be wrong for very high
>   clock rates
> 
> Changes in v12:
> - Add a comment to the timer driver about #pwm-cells
> - Combine/expand comments on rounding in xilinx_pwm_apply
> 
> Changes in v11:
> - Add comment about why we test for #pwm-cells
> - Clarify comment on generate out signal
> - Rename pwm variables to xilinx_pwm
> - Round like Uwe wants...
> - s/xilinx_timer/xilinx_pwm/ for non-common functions
> 
> 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
>   debugfs
> - 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
>   code.
> - 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
> - Rename TCSR_(SET|CLEAR) to TCSR_RUN_(SET|CLEAR)
> - 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
> 
>  MAINTAINERS                        |   6 +
>  arch/microblaze/kernel/timer.c     |   4 +
>  drivers/pwm/Kconfig                |  14 ++
>  drivers/pwm/Makefile               |   1 +
>  drivers/pwm/pwm-xilinx.c           | 321 +++++++++++++++++++++++++++++
>  include/clocksource/timer-xilinx.h |  73 +++++++
>  6 files changed, 419 insertions(+)
>  create mode 100644 drivers/pwm/pwm-xilinx.c
>  create mode 100644 include/clocksource/timer-xilinx.h

Applied with Uwe's s/>= 1 GHz/> 1 GHz/ ask applied. I've also changed
the MODULE_LICENSE string to just "GPL" since that's what checkpatch
requested.

Thanks,
Thierry
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