Re: [PATCH v3] mfd: syscon: Add Spreadtrum physical regmap bus support

Baolin Wang
2020-04-27T07:23:53Z

Hi Arnd and Lee,

On Tue, Apr 21, 2020 at 10:13 PM Baolin Wang <baolin.wang7@gmail.com> wrote:
>
> Some platforms such as Spreadtrum platform, define a special method to
> update bits of the registers instead of read-modify-write, which means
> we should use a physical regmap bus to define the reg_update_bits()
> operation instead of the MMIO regmap bus. Thus we can register a new
> physical regmap bus into syscon core to support this.
>
> Signed-off-by: Baolin Wang <baolin.wang7@gmail.com>

Do you have any comments for this patch? Thanks.

> ---
> Changes from v2:
> - Fix building errors without enabling CONFIG_ARCH_SPRD.
>
> Changes from v1:
> - Add WARN_ONCE() for seting bits and clearing bits at the same time.
> - Remove the Spreadtrum SoC syscon driver, instead moving the regmap_bus
> instance into syscon.c driver.
>
> Changes from RFC v2:
> - Drop regmap change, which was applied by Mark.
> - Add more information about how to use set/clear.
> - Add checking to ensure the platform is compatible with
> using a new physical regmap bus.
>
> Changes from RFC v1:
> - Add new helper to registers a physical regmap bus instead of
> using the MMIO bus.
> ---
> drivers/mfd/syscon.c | 83 ++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 81 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
> index 3a97816d0cba..ca91b7770e1a 100644
> --- a/drivers/mfd/syscon.c
> +++ b/drivers/mfd/syscon.c
> @@ -40,6 +40,72 @@ static const struct regmap_config syscon_regmap_config = {
> .reg_stride = 4,
> };
>
> +#if IS_ENABLED(CONFIG_ARCH_SPRD)
> +#define SPRD_REG_SET_OFFSET 0x1000
> +#define SPRD_REG_CLR_OFFSET 0x2000
> +
> +/*
> + * The Spreadtrum platform defines a special set/clear method to update
> + * registers' bits, which means it can write values to the register's SET
> + * address (offset is 0x1000) to set bits, and write values to the register's
> + * CLEAR address (offset is 0x2000) to clear bits.
> + *
> + * This set/clear method can help to remove the race of accessing the global
> + * registers between the multiple subsystems instead of using hardware
> + * spinlocks.
> + *
> + * Note: there is a potential risk when users want to set and clear bits
> + * at the same time, since the set/clear method will always do bits setting
> + * before bits clearing, which may cause some unexpected results if the
> + * operation sequence is strict. Thus we recommend that do not set and
> + * clear bits at the same time if you are not sure about the results.
> + */
> +static int sprd_syscon_update_bits(void *context, unsigned int reg,
> + unsigned int mask, unsigned int val)
> +{
> + void __iomem *base = context;
> + unsigned int set, clr;
> +
> + set = val & mask;
> + clr = ~set & mask;
> +
> + if (set)
> + writel(set, base + reg + SPRD_REG_SET_OFFSET);
> +
> + if (clr)
> + writel(clr, base + reg + SPRD_REG_CLR_OFFSET);
> +
> + WARN_ONCE(set && clr, "%s: non-atomic update", __func__);
> + return 0;
> +}
> +
> +static int sprd_syscon_read(void *context, unsigned int reg, unsigned int *val)
> +{
> + void __iomem *base = context;
> +
> + *val = readl(base + reg);
> + return 0;
> +}
> +
> +static int sprd_syscon_write(void *context, unsigned int reg, unsigned int val)
> +{
> + void __iomem *base = context;
> +
> + writel(val, base + reg);
> + return 0;
> +}
> +#endif
> +
> +static struct regmap_bus sprd_syscon_regmap_bus = {
> +#if IS_ENABLED(CONFIG_ARCH_SPRD)
> + .fast_io = true,
> + .reg_write = sprd_syscon_write,
> + .reg_read = sprd_syscon_read,
> + .reg_update_bits = sprd_syscon_update_bits,
> + .val_format_endian_default = REGMAP_ENDIAN_LITTLE,
> +#endif
> +};
> +
> static struct syscon *of_syscon_register(struct device_node *np, bool check_clk)
> {
> struct clk *clk;
> @@ -50,6 +116,7 @@ static struct syscon *of_syscon_register(struct device_node *np, bool check_clk)
> int ret;
> struct regmap_config syscon_config = syscon_regmap_config;
> struct resource res;
> + bool use_phy_regmap_bus = false;
>
> syscon = kzalloc(sizeof(*syscon), GFP_KERNEL);
> if (!syscon)
> @@ -106,14 +173,26 @@ static struct syscon *of_syscon_register(struct device_node *np, bool check_clk)
> syscon_config.val_bits = reg_io_width * 8;
> syscon_config.max_register = resource_size(&res) - reg_io_width;
>
> - regmap = regmap_init_mmio(NULL, base, &syscon_config);
> + /*
> + * The Spreadtrum syscon need register a real physical regmap bus
> + * with new atomic bits updating operation instead of using
> + * read-modify-write.
> + */
> + if (IS_ENABLED(CONFIG_ARCH_SPRD) &&
> + of_device_is_compatible(np, "sprd,atomic-syscon")) {
> + use_phy_regmap_bus = true;
> + regmap = regmap_init(NULL, &sprd_syscon_regmap_bus, base,
> + &syscon_config);
> + } else {
> + regmap = regmap_init_mmio(NULL, base, &syscon_config);
> + }
> if (IS_ERR(regmap)) {
> pr_err("regmap init failed\n");
> ret = PTR_ERR(regmap);
> goto err_regmap;
> }
>
> - if (check_clk) {
> + if (!use_phy_regmap_bus && check_clk) {
> clk = of_clk_get(np, 0);
> if (IS_ERR(clk)) {
> ret = PTR_ERR(clk);
> --
> 2.17.1
>

--
Baolin Wang