Re: [PATCH 08/12] regmap: indirect: Add indirect regmap support

[Marco Pagani <marpagan@redhat.com>]

On 2022-11-08 15:43, Ilpo Järvinen wrote:
> Add support for indirect register access via a regmap interface.
> 
> Indirect register access is a generic way to access registers directly.
> One use case is accessing registers on Intel FPGA IPs with e.g. PMCI or
> HSSI.
> 
> Co-developed-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
> Signed-off-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> ---
>  drivers/base/regmap/Kconfig           |   3 +
>  drivers/base/regmap/Makefile          |   1 +
>  drivers/base/regmap/regmap-indirect.c | 128 ++++++++++++++++++++++++++
>  include/linux/regmap.h                |  55 +++++++++++
>  4 files changed, 187 insertions(+)
>  create mode 100644 drivers/base/regmap/regmap-indirect.c
> 
> diff --git a/drivers/base/regmap/Kconfig b/drivers/base/regmap/Kconfig
> index 159bac6c5046..94e5ca5434cf 100644
> --- a/drivers/base/regmap/Kconfig
> +++ b/drivers/base/regmap/Kconfig
> @@ -65,3 +65,6 @@ config REGMAP_I3C
>  config REGMAP_SPI_AVMM
>  	tristate
>  	depends on SPI
> +
> +config REGMAP_INDIRECT
> +	tristate
> diff --git a/drivers/base/regmap/Makefile b/drivers/base/regmap/Makefile
> index 11facb32a027..6221a4740806 100644
> --- a/drivers/base/regmap/Makefile
> +++ b/drivers/base/regmap/Makefile
> @@ -20,3 +20,4 @@ obj-$(CONFIG_REGMAP_SCCB) += regmap-sccb.o
>  obj-$(CONFIG_REGMAP_I3C) += regmap-i3c.o
>  obj-$(CONFIG_REGMAP_SPI_AVMM) += regmap-spi-avmm.o
>  obj-$(CONFIG_REGMAP_MDIO) += regmap-mdio.o
> +obj-$(CONFIG_REGMAP_INDIRECT) += regmap-indirect.o
> diff --git a/drivers/base/regmap/regmap-indirect.c b/drivers/base/regmap/regmap-indirect.c
> new file mode 100644
> index 000000000000..3ceb0c044c7c
> --- /dev/null
> +++ b/drivers/base/regmap/regmap-indirect.c
> @@ -0,0 +1,128 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Indirect Register Access.
> + *
> + * Copyright (C) 2020-2022 Intel Corporation, Inc.
> + */
> +#include <linux/debugfs.h>
> +#include <linux/device.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/regmap.h>
> +#include <linux/seq_file.h>
> +#include <linux/slab.h>
> +
> +struct indirect_ctx {
> +	void __iomem *base;
> +	struct device *dev;
> +	const struct regmap_indirect_cfg *indirect_cfg;
> +};
> +
> +static int indirect_bus_idle_cmd(struct indirect_ctx *ctx)
> +{
> +	unsigned int cmd;
> +	int ret;
> +
> +	writel(ctx->indirect_cfg->idle_cmd, ctx->base + ctx->indirect_cfg->cmd_offset);
> +
> +	ret = readl_poll_timeout(ctx->base + ctx->indirect_cfg->cmd_offset, cmd,
> +				 cmd == ctx->indirect_cfg->idle_cmd,
> +				 ctx->indirect_cfg->sleep_us, ctx->indirect_cfg->timeout_us);
> +	if (ret)
> +		dev_err(ctx->dev, "timed out waiting idle cmd (residual cmd=0x%x)\n", cmd);
> +
> +	return ret;
> +}
> +
> +static int indirect_bus_reg_read(void *context, unsigned int reg,
> +				     unsigned int *val)
> +{
> +	struct indirect_ctx *ctx = context;
> +	unsigned int cmd, ack, tmpval;
> +	int ret;
> +
> +	cmd = readl(ctx->base + ctx->indirect_cfg->cmd_offset);
> +	if (cmd != ctx->indirect_cfg->idle_cmd)
> +		dev_warn(ctx->dev, "residual cmd 0x%x on read entry\n", cmd);
> +
> +	writel(reg, ctx->base + ctx->indirect_cfg->addr_offset);
> +	writel(ctx->indirect_cfg->read_cmd, ctx->base + ctx->indirect_cfg->cmd_offset);
> +
> +	ret = readl_poll_timeout(ctx->base + ctx->indirect_cfg->ack_offset, ack,
> +				 (ack & ctx->indirect_cfg->ack_mask) == ctx->indirect_cfg->ack_mask,
> +				 ctx->indirect_cfg->sleep_us, ctx->indirect_cfg->timeout_us);
> +	if (ret) {
> +		dev_err(ctx->dev, "read timed out on reg 0x%x ack 0x%x\n", reg, ack);
> +		goto out;
> +	}
> +
> +	tmpval = readl(ctx->base + ctx->indirect_cfg->read_offset);
> +
> +	if (indirect_bus_idle_cmd(ctx)) {
> +		if (!ret)

Could you please explain why it is necessary to insert an idle_cmd after each
bus read or write? Do the bus read and write methods assume there will be an 
idle_cmd in the cmd register at initialization? Is this assumption safe if the
device detaches and reattaches? Isn't the "if (!ret)" check redundant since
ret is always == 0?

> +			ret = -ETIMEDOUT;
> +		goto out;
> +	}
> +
> +	*val = tmpval;
> +out:
> +	return ret;
> +}
> +
> +static int indirect_bus_reg_write(void *context, unsigned int reg,
> +				      unsigned int val)
> +{
> +	struct indirect_ctx *ctx = context;
> +	unsigned int cmd, ack;
> +	int ret;
> +
> +	cmd = readl(ctx->base + ctx->indirect_cfg->cmd_offset);
> +	if (cmd != ctx->indirect_cfg->idle_cmd)
> +		dev_warn(ctx->dev, "residual cmd 0x%x on write entry\n", cmd);
> +
> +	writel(val, ctx->base + ctx->indirect_cfg->write_offset);
> +	writel(reg, ctx->base + ctx->indirect_cfg->addr_offset);
> +	writel(ctx->indirect_cfg->write_cmd, ctx->base + ctx->indirect_cfg->cmd_offset);
> +
> +	ret = readl_poll_timeout(ctx->base + ctx->indirect_cfg->ack_offset, ack,
> +				 (ack & ctx->indirect_cfg->ack_mask) == ctx->indirect_cfg->ack_mask,
> +				 ctx->indirect_cfg->sleep_us, ctx->indirect_cfg->timeout_us);
> +	if (ret)
> +		dev_err(ctx->dev, "write timed out on reg 0x%x ack 0x%x\n", reg, ack);
> +
> +	if (indirect_bus_idle_cmd(ctx)) {
> +		if (!ret)
> +			ret = -ETIMEDOUT;
> +	}
> +
> +	return ret;
> +}
> +
> +static const struct regmap_bus indirect_bus = {
> +	.reg_write = indirect_bus_reg_write,
> +	.reg_read =  indirect_bus_reg_read,
> +};
> +
> +struct regmap *__devm_regmap_init_indirect(struct device *dev,
> +					   void __iomem *base,
> +					   struct regmap_config *cfg,
> +					   struct lock_class_key *lock_key,
> +					   const char *lock_name)
> +{
> +	struct indirect_ctx *ctx;
> +
> +	ctx = devm_kzalloc(dev, sizeof(*ctx), GFP_KERNEL);
> +	if (!ctx)
> +		return NULL;
> +
> +	ctx->base = base;
> +	ctx->dev = dev;
> +	ctx->indirect_cfg = cfg->indirect_cfg;
> +
> +	return __devm_regmap_init(dev, &indirect_bus, ctx, cfg, lock_key, lock_name);
> +}
> +EXPORT_SYMBOL_GPL(__devm_regmap_init_indirect);
> +
> +MODULE_DESCRIPTION("Indirect Register Access");
> +MODULE_AUTHOR("Intel Corporation");
> +MODULE_LICENSE("GPL");
> diff --git a/include/linux/regmap.h b/include/linux/regmap.h
> index ca3434dca3a0..adaa7bca4f60 100644
> --- a/include/linux/regmap.h
> +++ b/include/linux/regmap.h
> @@ -190,6 +190,41 @@ enum regmap_endian {
>  	REGMAP_ENDIAN_NATIVE,
>  };
>  
> +/**
> + * struct regmap_indirect_cfg - A configuration for indirect register access
> + *
> + * @cmd_offset: Command register offset
> + * @idle_cmd: Idle command
> + * @read_cmd: Read command
> + * @write_cmd: Write command
> + *
> + * @ack_offset: Command acknowledgment register offset
> + * @ack_mask: Command acknowledgment bit mask
> + *
> + * @addr_offset: Address register offset
> + * @read_offset: Read register offset
> + * @write_offset: Write register offset
> + *
> + * @sleep_us: Command wait sleep (usecs)
> + * @timeout_us: Command timeout (usecs)
> + */
> +struct regmap_indirect_cfg {
> +	unsigned int cmd_offset;
> +	u32 idle_cmd;
> +	u32 read_cmd;
> +	u32 write_cmd;
> +
> +	unsigned int ack_offset;
> +	u32 ack_mask;
> +
> +	unsigned int addr_offset;
> +	unsigned int read_offset;
> +	unsigned int write_offset;
> +
> +	unsigned long sleep_us;
> +	unsigned long timeout_us;
> +};
> +
>  /**
>   * struct regmap_range - A register range, used for access related checks
>   *                       (readable/writeable/volatile/precious checks)
> @@ -431,6 +466,8 @@ struct regmap_config {
>  	const struct regmap_range_cfg *ranges;
>  	unsigned int num_ranges;
>  
> +	const struct regmap_indirect_cfg *indirect_cfg;
> +
>  	bool use_hwlock;
>  	bool use_raw_spinlock;
>  	unsigned int hwlock_id;
> @@ -693,6 +730,12 @@ struct regmap *__devm_regmap_init_spi_avmm(struct spi_device *spi,
>  					   const struct regmap_config *config,
>  					   struct lock_class_key *lock_key,
>  					   const char *lock_name);
> +struct regmap *__devm_regmap_init_indirect(struct device *dev,
> +					   void __iomem *base,
> +					   struct regmap_config *cfg,
> +					   struct lock_class_key *lock_key,
> +					   const char *lock_name);
> +
>  /*
>   * Wrapper for regmap_init macros to include a unique lockdep key and name
>   * for each call. No-op if CONFIG_LOCKDEP is not set.
> @@ -1148,6 +1191,18 @@ bool regmap_ac97_default_volatile(struct device *dev, unsigned int reg);
>  	__regmap_lockdep_wrapper(__devm_regmap_init_spi_avmm, #config,	\
>  				 spi, config)
>  
> +/**
> + * devm_regmap_init_indirect - create a regmap for indirect register access
> + * @dev: device creating the regmap
> + * @base: __iomem point to base of memory with mailbox
> + * @cfg: regmap_config describing interface
> + *
> + * Return: 0 on success, negative error code otherwise.
> + */
> +#define devm_regmap_init_indirect(dev, base, config)			\
> +	__regmap_lockdep_wrapper(__devm_regmap_init_indirect, #config,	\
> +				 dev, base, config)
> +
>  int regmap_mmio_attach_clk(struct regmap *map, struct clk *clk);
>  void regmap_mmio_detach_clk(struct regmap *map);
>  void regmap_exit(struct regmap *map);

Thanks,
Marco