Re: [PATCH v2] drivers/soc/litex: support 32-bit subregisters, 64-bit CPUs

From: Stafford Horne
Date: Wed Dec 23 2020 - 16:48:52 EST

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In reply to: Gabriel Somlo: "[PATCH v2] drivers/soc/litex: support 32-bit subregisters, 64-bit CPUs"
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On Tue, Dec 22, 2020 at 05:04:46PM -0500, Gabriel Somlo wrote:
> The upstream LiteX project now defaults to using 32-bit subregisters
> (see https://github.com/enjoy-digital/litex/commit/a2b71fde).
>
> This patch expands on commit 22447a99c97e, adding support for handling
> both 8 and 32 bit LiteX CSR (MMIO) subregisters, as controlled by the
> LITEX_SUBREG_SIZE Kconfig option.

The commit should be written in the format:
22447a99c97e ("drivers/soc/litex: add LiteX SoC Controller driver")

> Signed-off-by: Gabriel Somlo <gsomlo@xxxxxxxxx>

Gabriel thanks for submitting this.

> ---
>
> Notes v2:
> - fix typo (s/u32/u64/) in litex_read64().
>
> Notes v1:
> - LITEX_SUBREG_SIZE now provided by Kconfig.
> - it's not LITEX_REG_SIZE, but rather LITEX_SUBREG_ALIGN!
> - move litex_[get|set]_reg() to include/linux/litex.h and mark
> them as "static inline";
> - redo litex_[read|write][8|16|32|64]() using litex_[get|set]_reg()
> (compiler should produce code as efficient as hardcoded shifts,
> but also automatically matching LITEX_SUBREG_SIZE).
>
> drivers/soc/litex/Kconfig | 12 ++
> drivers/soc/litex/litex_soc_ctrl.c | 76 +-----------
> include/linux/litex.h | 179 +++++++++++++++++++++--------
> 3 files changed, 143 insertions(+), 124 deletions(-)
>
> diff --git a/drivers/soc/litex/Kconfig b/drivers/soc/litex/Kconfig
> index 7c6b009b6f6c..973f8d2fe1a7 100644
> --- a/drivers/soc/litex/Kconfig
> +++ b/drivers/soc/litex/Kconfig
> @@ -16,4 +16,16 @@ config LITEX_SOC_CONTROLLER
> All drivers that use functions from litex.h must depend on
> LITEX.
>
> +config LITEX_SUBREG_SIZE
> + int "Size of a LiteX CSR subregister, in bytes"
> + depends on LITEX
> + range 1 4
> + default 4
> + help
> + LiteX MMIO registers (referred to as Configuration and Status
> + registers, or CSRs) are spread across adjacent 8- or 32-bit
> + subregisters, located at 32-bit aligned MMIO addresses. Use
> + this to select the appropriate size (1 or 4 bytes) matching
> + your particular LiteX build.

Could this config be moved to device tree? I see not as you want to compiler to
use hard coded shifts. Can you mention this in the commit message not just
the v1 notes?

> endmenu
> diff --git a/drivers/soc/litex/litex_soc_ctrl.c b/drivers/soc/litex/litex_soc_ctrl.c
> index 1217cafdfd4d..da17ba56b795 100644
> --- a/drivers/soc/litex/litex_soc_ctrl.c
> +++ b/drivers/soc/litex/litex_soc_ctrl.c
> @@ -16,79 +16,6 @@
> #include <linux/errno.h>
> #include <linux/io.h>
>
> -/*
> - * LiteX SoC Generator, depending on the configuration, can split a single
> - * logical CSR (Control&Status Register) into a series of consecutive physical
> - * registers.
> - *
> - * For example, in the configuration with 8-bit CSR Bus, 32-bit aligned (the
> - * default one for 32-bit CPUs) a 32-bit logical CSR will be generated as four
> - * 32-bit physical registers, each one containing one byte of meaningful data.
> - *
> - * For details see: https://github.com/enjoy-digital/litex/wiki/CSR-Bus
> - *
> - * The purpose of `litex_set_reg`/`litex_get_reg` is to implement the logic
> - * of writing to/reading from the LiteX CSR in a single place that can be
> - * then reused by all LiteX drivers.
> - */
> -
> -/**
> - * litex_set_reg() - Writes the value to the LiteX CSR (Control&Status Register)
> - * @reg: Address of the CSR
> - * @reg_size: The width of the CSR expressed in the number of bytes
> - * @val: Value to be written to the CSR
> - *
> - * In the currently supported LiteX configuration (8-bit CSR Bus, 32-bit aligned),
> - * a 32-bit LiteX CSR is generated as 4 consecutive 32-bit physical registers,
> - * each one containing one byte of meaningful data.
> - *
> - * This function splits a single possibly multi-byte write into a series of
> - * single-byte writes with a proper offset.
> - */
> -void litex_set_reg(void __iomem *reg, unsigned long reg_size,
> - unsigned long val)
> -{
> - unsigned long shifted_data, shift, i;
> -
> - for (i = 0; i < reg_size; ++i) {
> - shift = ((reg_size - i - 1) * LITEX_SUBREG_SIZE_BIT);
> - shifted_data = val >> shift;
> -
> - WRITE_LITEX_SUBREGISTER(shifted_data, reg, i);
> - }
> -}
> -EXPORT_SYMBOL_GPL(litex_set_reg);
> -
> -/**
> - * litex_get_reg() - Reads the value of the LiteX CSR (Control&Status Register)
> - * @reg: Address of the CSR
> - * @reg_size: The width of the CSR expressed in the number of bytes
> - *
> - * Return: Value read from the CSR
> - *
> - * In the currently supported LiteX configuration (8-bit CSR Bus, 32-bit aligned),
> - * a 32-bit LiteX CSR is generated as 4 consecutive 32-bit physical registers,
> - * each one containing one byte of meaningful data.
> - *
> - * This function generates a series of single-byte reads with a proper offset
> - * and joins their results into a single multi-byte value.
> - */
> -unsigned long litex_get_reg(void __iomem *reg, unsigned long reg_size)
> -{
> - unsigned long shifted_data, shift, i;
> - unsigned long result = 0;
> -
> - for (i = 0; i < reg_size; ++i) {
> - shifted_data = READ_LITEX_SUBREGISTER(reg, i);
> -
> - shift = ((reg_size - i - 1) * LITEX_SUBREG_SIZE_BIT);
> - result |= (shifted_data << shift);
> - }
> -
> - return result;
> -}
> -EXPORT_SYMBOL_GPL(litex_get_reg);
> -
> #define SCRATCH_REG_OFF 0x04
> #define SCRATCH_REG_VALUE 0x12345678
> #define SCRATCH_TEST_VALUE 0xdeadbeef
> @@ -131,7 +58,8 @@ static int litex_check_csr_access(void __iomem *reg_addr)
> /* restore original value of the SCRATCH register */
> litex_write32(reg_addr + SCRATCH_REG_OFF, SCRATCH_REG_VALUE);
>
> - pr_info("LiteX SoC Controller driver initialized");
> + pr_info("LiteX SoC Controller driver initialized: subreg:%d, align:%d",
> + LITEX_SUBREG_SIZE, LITEX_SUBREG_ALIGN);
>
> return 0;
> }
> diff --git a/include/linux/litex.h b/include/linux/litex.h
> index 40f5be503593..71f8110ed98d 100644
> --- a/include/linux/litex.h
> +++ b/include/linux/litex.h
> @@ -3,9 +3,6 @@
> * Common LiteX header providing
> * helper functions for accessing CSRs.
> *
> - * Implementation of the functions is provided by
> - * the LiteX SoC Controller driver.
> - *
> * Copyright (C) 2019-2020 Antmicro <www.antmicro.com>
> */
>
> @@ -13,90 +10,172 @@
> #define _LINUX_LITEX_H
>
> #include <linux/io.h>
> -#include <linux/types.h>
> -#include <linux/compiler_types.h>
>
> -/*
> - * The parameters below are true for LiteX SoCs configured for 8-bit CSR Bus,
> - * 32-bit aligned.
> - *
> - * Supporting other configurations will require extending the logic in this
> - * header and in the LiteX SoC controller driver.
> - */
> -#define LITEX_REG_SIZE 0x4
> -#define LITEX_SUBREG_SIZE 0x1
> +/* LiteX SoCs support 8- or 32-bit CSR Bus data width (i.e., subreg. size) */
> +#if defined(CONFIG_LITEX_SUBREG_SIZE) && \
> + (CONFIG_LITEX_SUBREG_SIZE == 1 || CONFIG_LITEX_SUBREG_SIZE == 4)
> +#define LITEX_SUBREG_SIZE CONFIG_LITEX_SUBREG_SIZE
> +#else
> +#error LiteX subregister size (LITEX_SUBREG_SIZE) must be 4 or 1!
> +#endif
> #define LITEX_SUBREG_SIZE_BIT (LITEX_SUBREG_SIZE * 8)
>
> -#define WRITE_LITEX_SUBREGISTER(val, base_offset, subreg_id) \
> - writel((u32 __force)cpu_to_le32(val), base_offset + (LITEX_REG_SIZE * subreg_id))
> +/* LiteX subregisters of any width are always aligned on a 4-byte boundary */
> +#define LITEX_SUBREG_ALIGN 0x4
>
> -#define READ_LITEX_SUBREGISTER(base_offset, subreg_id) \
> - le32_to_cpu((__le32 __force)readl(base_offset + (LITEX_REG_SIZE * subreg_id)))
> +static inline void _write_litex_subregister(u32 val, void __iomem *addr)
> +{
> + writel((u32 __force)cpu_to_le32(val), addr);
> +}
>
> -void litex_set_reg(void __iomem *reg, unsigned long reg_sz, unsigned long val);
> +static inline u32 _read_litex_subregister(void __iomem *addr)
> +{
> + return le32_to_cpu((__le32 __force)readl(addr));
> +}
>
> -unsigned long litex_get_reg(void __iomem *reg, unsigned long reg_sz);
> +#define _WRITE_LITEX_SUBREGISTER(val, base_offset, subreg_id) \
> + _write_litex_subregister(val, (base_offset) + \
> + LITEX_SUBREG_ALIGN * (subreg_id))
> +
> +#define _READ_LITEX_SUBREGISTER(base_offset, subreg_id) \
> + _read_litex_subregister((base_offset) + \
> + LITEX_SUBREG_ALIGN * (subreg_id))
> +
> +/*
> + * LiteX SoC Generator, depending on the configuration, can split a single
> + * logical CSR (Control&Status Register) into a series of consecutive physical
> + * registers.
> + *
> + * For example, in the configuration with 8-bit CSR Bus, 32-bit aligned
> + * a 32-bit logical CSR will be generated as four 32-bit physical registers,
> + * each one containing one byte of meaningful data.
> + *
> + * For details see: https://github.com/enjoy-digital/litex/wiki/CSR-Bus
> + */
> +
> +/* number of LiteX subregisters needed to store a register of given reg_size */
> +#define _litex_num_subregs(reg_size) \
> + (((reg_size) - 1) / LITEX_SUBREG_SIZE + 1)
> +
> +/* since the number of 4-byte aligned subregisters required to store a single
> + * LiteX CSR (MMIO) register varies with LITEX_SUBREG_SIZE, the offset of the
> + * next adjacent LiteX CSR register w.r.t. the offset of the current one also
> + * depends on how many subregisters the latter is spread across
> + */
> +#define _next_reg_off(off, size) \
> + ((off) + _litex_num_subregs(size) * LITEX_SUBREG_ALIGN)
> +
> +/*
> + * The purpose of `litex_set_reg`/`litex_get_reg` is to implement the logic
> + * of writing to/reading from the LiteX CSR in a single place that can be
> + * then reused by all LiteX drivers.
> + */
> +
> +/**
> + * litex_set_reg() - Writes the value to the LiteX CSR (Control&Status Register)
> + * @reg: Address of the CSR
> + * @reg_size: The width of the CSR expressed in the number of bytes
> + * @val: Value to be written to the CSR
> + *
> + * This function splits a single (possibly multi-byte) LiteX CSR write into
> + * a series of subregister writes with a proper offset.
> + */
> +static inline void litex_set_reg(void __iomem *reg, ulong reg_size, ulong val)
> +{
> + u8 ns, shift, i;
> +
> + ns = _litex_num_subregs(reg_size);
> + for (i = 0; i < ns; i++) {
> + shift = LITEX_SUBREG_SIZE_BIT * (ns - 1 - i);
> + _write_litex_subregister(val >> shift, reg);
> + reg += LITEX_SUBREG_ALIGN;
> + }
> +}
> +
> +/**
> + * litex_get_reg() - Reads the value of the LiteX CSR (Control&Status Register)
> + * @reg: Address of the CSR
> + * @reg_size: The width of the CSR expressed in the number of bytes
> + *
> + * Return: Value read from the CSR
> + *
> + * This function generates a series of subregister reads with a proper offset
> + * and joins their results into a single (possibly multi-byte) LiteX CSR value.
> + */
> +static inline ulong litex_get_reg(void __iomem *reg, ulong reg_size)
> +{
> + ulong r;
> + u8 i;
> +
> + r = _read_litex_subregister(reg);
> + for (i = 1; i < _litex_num_subregs(reg_size); i++) {
> + r <<= LITEX_SUBREG_SIZE_BIT;
> + reg += LITEX_SUBREG_ALIGN;
> + r |= _read_litex_subregister(reg);
> + }
> + return r;
> +}

Why move these definitions from the .c file to the .h file and make the comments
smaller? This is not mentioned in the commit message? Perhaps the move
(non-functional change) should be moved in a separate commit?

Also, this is causing problems building on 32-bit systems. I get a warning:

In file included from drivers/tty/serial/liteuart.c:9:
./include/linux/litex.h: In function ‘litex_get_reg’:
./include/linux/litex.h:112:5: warning: left shift count >= width of type [-Wshift-count-overflow]
112 | r <<= LITEX_SUBREG_SIZE_BIT;
| ^~~

> static inline void litex_write8(void __iomem *reg, u8 val)
> {
> - WRITE_LITEX_SUBREGISTER(val, reg, 0);
> + litex_set_reg(reg, sizeof(u8), val);
> }
>
> static inline void litex_write16(void __iomem *reg, u16 val)
> {
> - WRITE_LITEX_SUBREGISTER(val >> 8, reg, 0);
> - WRITE_LITEX_SUBREGISTER(val, reg, 1);
> + litex_set_reg(reg, sizeof(u16), val);
> }
>
> static inline void litex_write32(void __iomem *reg, u32 val)
> {
> - WRITE_LITEX_SUBREGISTER(val >> 24, reg, 0);
> - WRITE_LITEX_SUBREGISTER(val >> 16, reg, 1);
> - WRITE_LITEX_SUBREGISTER(val >> 8, reg, 2);
> - WRITE_LITEX_SUBREGISTER(val, reg, 3);
> + litex_set_reg(reg, sizeof(u32), val);
> }
>
> static inline void litex_write64(void __iomem *reg, u64 val)
> {
> - WRITE_LITEX_SUBREGISTER(val >> 56, reg, 0);
> - WRITE_LITEX_SUBREGISTER(val >> 48, reg, 1);
> - WRITE_LITEX_SUBREGISTER(val >> 40, reg, 2);
> - WRITE_LITEX_SUBREGISTER(val >> 32, reg, 3);
> - WRITE_LITEX_SUBREGISTER(val >> 24, reg, 4);
> - WRITE_LITEX_SUBREGISTER(val >> 16, reg, 5);
> - WRITE_LITEX_SUBREGISTER(val >> 8, reg, 6);
> - WRITE_LITEX_SUBREGISTER(val, reg, 7);
> +#ifdef CONFIG_64BIT
> + litex_set_reg(reg, sizeof(u64), val);
I think 64-bit support should be split to a separate patch too.

Look at: https://www.kernel.org/doc/html/v4.17/process/submitting-patches.html#separate-your-changes

> +#else
> + _WRITE_LITEX_SUBREGISTER(val >> 56, reg, 0);
> + _WRITE_LITEX_SUBREGISTER(val >> 48, reg, 1);
> + _WRITE_LITEX_SUBREGISTER(val >> 40, reg, 2);
> + _WRITE_LITEX_SUBREGISTER(val >> 32, reg, 3);
> + _WRITE_LITEX_SUBREGISTER(val >> 24, reg, 4);
> + _WRITE_LITEX_SUBREGISTER(val >> 16, reg, 5);
> + _WRITE_LITEX_SUBREGISTER(val >> 8, reg, 6);
> + _WRITE_LITEX_SUBREGISTER(val, reg, 7);
> +#endif
> }
>
> static inline u8 litex_read8(void __iomem *reg)
> {
> - return READ_LITEX_SUBREGISTER(reg, 0);
> + return litex_get_reg(reg, sizeof(u8));
> }
>
> static inline u16 litex_read16(void __iomem *reg)
> {
> - return (READ_LITEX_SUBREGISTER(reg, 0) << 8)
> - | (READ_LITEX_SUBREGISTER(reg, 1));
> + return litex_get_reg(reg, sizeof(u16));
> }
>
> static inline u32 litex_read32(void __iomem *reg)
> {
> - return (READ_LITEX_SUBREGISTER(reg, 0) << 24)
> - | (READ_LITEX_SUBREGISTER(reg, 1) << 16)
> - | (READ_LITEX_SUBREGISTER(reg, 2) << 8)
> - | (READ_LITEX_SUBREGISTER(reg, 3));
> + return litex_get_reg(reg, sizeof(u32));
> }
>
> static inline u64 litex_read64(void __iomem *reg)
> {
> - return ((u64)READ_LITEX_SUBREGISTER(reg, 0) << 56)
> - | ((u64)READ_LITEX_SUBREGISTER(reg, 1) << 48)
> - | ((u64)READ_LITEX_SUBREGISTER(reg, 2) << 40)
> - | ((u64)READ_LITEX_SUBREGISTER(reg, 3) << 32)
> - | ((u64)READ_LITEX_SUBREGISTER(reg, 4) << 24)
> - | ((u64)READ_LITEX_SUBREGISTER(reg, 5) << 16)
> - | ((u64)READ_LITEX_SUBREGISTER(reg, 6) << 8)
> - | ((u64)READ_LITEX_SUBREGISTER(reg, 7));
> +#ifdef CONFIG_64BIT
> + return litex_get_reg(reg, sizeof(u64));
> +#else
> + return ((u64)_READ_LITEX_SUBREGISTER(reg, 0) << 56)
> + | ((u64)_READ_LITEX_SUBREGISTER(reg, 1) << 48)
> + | ((u64)_READ_LITEX_SUBREGISTER(reg, 2) << 40)
> + | ((u64)_READ_LITEX_SUBREGISTER(reg, 3) << 32)
> + | ((u64)_READ_LITEX_SUBREGISTER(reg, 4) << 24)
> + | ((u64)_READ_LITEX_SUBREGISTER(reg, 5) << 16)
> + | ((u64)_READ_LITEX_SUBREGISTER(reg, 6) << 8)
> + | ((u64)_READ_LITEX_SUBREGISTER(reg, 7));
> +#endif
> }
>
> #endif /* _LINUX_LITEX_H */
> --
> 2.26.2
>

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