Re: [PATCH v4 2/3] clocksource: Rewrite Xilinx AXI timer driver

[Sean Anderson]

On 6/1/21 4:47 AM, Lee Jones wrote:
> On Fri, 28 May 2021, 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 have taken place in the
>> initialization:
>>
>> - 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.
>> - 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.
>>
>> Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxx>
>> ---
>> This has been tested on microblaze qemu.
>>
>> Changes in v4:
>> - Break out clock* drivers into their own file
>>
>>   arch/microblaze/kernel/Makefile    |   3 +-
>>   arch/microblaze/kernel/timer.c     | 326 -----------------------------
>>   drivers/clocksource/Kconfig        |  11 +
>>   drivers/clocksource/Makefile       |   1 +
>>   drivers/clocksource/timer-xilinx.c | 300 ++++++++++++++++++++++++++
>>   drivers/mfd/Makefile               |   4 +
>>   drivers/mfd/xilinx-timer.c         | 147 +++++++++++++
>
> I'm confused!
>
>>   include/linux/mfd/xilinx-timer.h   | 134 ++++++++++++
>>   8 files changed, 598 insertions(+), 328 deletions(-)
>>   delete mode 100644 arch/microblaze/kernel/timer.c
>>   create mode 100644 drivers/clocksource/timer-xilinx.c
>>   create mode 100644 drivers/mfd/xilinx-timer.c
>>   create mode 100644 include/linux/mfd/xilinx-timer.h
>
> [...]
>
>> +// SPDX-License-Identifier: GPL-2.0+
>> +/*
>> + * Copyright (C) 2021 Sean Anderson <sean.anderson@xxxxxxxx>
>> + *
>> + * For Xilinx LogiCORE IP AXI Timer documentation, refer to DS764:
>> + * https://www.xilinx.com/support/documentation/ip_documentation/axi_timer/v1_03_a/axi_timer_ds764.pdf
>> + */
>> +
>> +#include <linux/clk.h>
>> +#include <linux/mfd/xilinx-timer.h>
>> +#include <linux/of.h>
>> +#include <asm/io.h>
>
> RED FLAG: You are not using the MFD API here.

Should I be?

>
>> +#define TCSR0	0x00
>> +#define TLR0	0x04
>> +#define TCR0	0x08
>> +#define TCSR1	0x10
>> +#define TLR1	0x14
>> +#define TCR1	0x18
>> +
>> +#define TCSR_MDT	BIT(0)
>> +#define TCSR_UDT	BIT(1)
>> +#define TCSR_GENT	BIT(2)
>> +#define TCSR_CAPT	BIT(3)
>> +#define TCSR_ARHT	BIT(4)
>> +#define TCSR_LOAD	BIT(5)
>> +#define TCSR_ENIT	BIT(6)
>> +#define TCSR_ENT	BIT(7)
>> +#define TCSR_TINT	BIT(8)
>> +#define TCSR_PWMA	BIT(9)
>> +#define TCSR_ENALL	BIT(10)
>> +#define TCSR_CASC	BIT(11)
>> +
>> +/* readl/writel wrappers to support BE systems */
>> +
>> +static u32 xilinx_ioread32be(const void __iomem *addr)
>> +{
>> +	return ioread32be(addr);
>> +}
>> +
>> +static void xilinx_iowrite32be(u32 value, void __iomem *addr)
>> +{
>> +	iowrite32be(value, addr);
>> +}
>> +
>> +static u32 xilinx_ioread32(const void __iomem *addr)
>> +{
>> +	return ioread32(addr);
>> +}
>> +
>> +static void xilinx_iowrite32(u32 value, void __iomem *addr)
>> +{
>> +	iowrite32(value, addr);
>> +}
>
> Abstraction for the sake of abstraction, is not allowed.
>
> Just use the io*() calls directly in-place.

Can't. The call signatures on some arches have volatile addr and some do
not. So without these wrappers, we will get warnings about how the
function has the wrong type.

>
>> +int xilinx_timer_tlr_cycles(struct xilinx_timer_priv *priv, u32 *tlr,
>> +			    u32 tcsr, u64 cycles)
>> +{
>> +	if (cycles < 2 || cycles > priv->max + 2)
>> +		return -ERANGE;
>> +
>> +	if (tcsr & TCSR_UDT)
>> +		*tlr = cycles - 2;
>> +	else
>> +		*tlr = priv->max - cycles + 2;
>> +
>> +	return 0;
>> +}
>> +
>> +int xilinx_timer_tlr_period(struct xilinx_timer_priv *priv, u32 *tlr,
>> +			    u32 tcsr, unsigned int period)
>> +{
>> +	u64 cycles = DIV_ROUND_DOWN_ULL((u64)period * clk_get_rate(priv->clk),
>> +					NSEC_PER_SEC);
>> +
>> +	return xilinx_timer_tlr_cycles(priv, tlr, tcsr, cycles);
>> +}
>> +
>> +unsigned int xilinx_timer_get_period(struct xilinx_timer_priv *priv,
>> +				     u32 tlr, u32 tcsr)
>> +{
>> +	u64 cycles;
>> +
>> +	if (tcsr & TCSR_UDT)
>> +		cycles = tlr + 2;
>> +	else
>> +		cycles = priv->max - tlr + 2;
>> +
>> +	return DIV_ROUND_UP_ULL(cycles * NSEC_PER_SEC,
>> +				clk_get_rate(priv->clk));
>> +}
>> +
>> +int xilinx_timer_common_init(struct device_node *np,
>> +			     struct xilinx_timer_priv *priv,
>> +			     u32 *one_timer)
>> +{
>> +	int ret;
>> +	u32 tcsr0, width;
>> +
>> +
>> +	priv->read = xilinx_ioread32;
>> +	priv->write = xilinx_iowrite32;
>> +	/*
>> +	 * If PWM mode is enabled, we should try not to disturb it. Use
>> +	 * CAPT since if PWM mode is enabled then MDT will be set as
>> +	 * well.
>> +	 *
>> +	 * First, clear CAPT and verify that it has been cleared
>> +	 */
>> +	tcsr0 = xilinx_timer_read(priv, TCSR0);
>> +	xilinx_timer_write(priv, tcsr0 & ~(TCSR_CAPT & swab(TCSR_CAPT)), TCSR0);
>> +	tcsr0 = xilinx_timer_read(priv, TCSR0);
>> +	if (tcsr0 & (TCSR_CAPT | swab(TCSR_CAPT))) {
>> +		pr_err("%pOF: cannot determine endianness\n", np);
>> +		return -EOPNOTSUPP;
>> +	}
>> +
>> +	/* Then check to make sure our write sticks */
>> +	xilinx_timer_write(priv, tcsr0 | TCSR_CAPT, TCSR0);
>> +	if (!(xilinx_timer_read(priv, TCSR0) & TCSR_CAPT)) {
>> +		priv->read = xilinx_ioread32be;
>> +		priv->write = xilinx_iowrite32be;
>> +	}
>> +
>> +	ret = of_property_read_u32(np, "xlnx,one-timer-only", one_timer);
>> +	if (ret) {
>> +		pr_err("%pOF: err %d: xlnx,one-timer-only\n", np, ret);
>> +		return ret;
>> +	} else if (*one_timer && *one_timer != 1) {
>> +		pr_err("%pOF: xlnx,one-timer-only must be 0 or 1\n", np);
>> +		return -EINVAL;
>> +	}
>> +
>> +	ret = of_property_read_u32(np, "xlnx,count-width", &width);
>> +	if (ret == -EINVAL) {
>> +		width = 32;
>> +	} else if (ret) {
>> +		pr_err("%pOF: err %d: xlnx,count-width\n", np, ret);
>> +		return ret;
>> +	} else if (width < 8 || width > 32) {
>> +		pr_err("%pOF: invalid counter width\n", np);
>> +		return -EINVAL;
>> +	}
>> +	priv->max = BIT_ULL(width) - 1;
>> +
>> +	return 0;
>> +}
>
> This is *all* timer stuff.
>
> What is your rationale for dumping this into MFD?

It was requested that common code for the timer and PWM drivers be
reused in some way. I stuck it in mfd because I wasn't sure where else
to put it. If you have a better location suggestion, I'm all ears

--Sean