Re: [PATCH v4 3/5] drivers/soc/litex: add LiteX SoC Controller driver

[Sam Ravnborg <sam@ravnborg.org>]

Hi Mateusz

A few drive-by comments - the soc area is not something I am well
versed in.

	Sam

On Thu, Apr 02, 2020 at 08:46:10AM +0200, Mateusz Holenko wrote:
> From: Pawel Czarnecki <pczarnecki@internships.antmicro.com>
> 
> This commit adds driver for the FPGA-based LiteX SoC
> Controller from LiteX SoC builder.
> 
> Co-developed-by: Mateusz Holenko <mholenko@antmicro.com>
> Signed-off-by: Mateusz Holenko <mholenko@antmicro.com>
> Signed-off-by: Pawel Czarnecki <pczarnecki@internships.antmicro.com>
> ---
> 
> Notes:
>     Changes in v4:
>     - fixed indent in Kconfig's help section
>     - fixed copyright header
>     - changed compatible to "litex,soc-controller"
>     - simplified litex_soc_ctrl_probe
>     - removed unnecessary litex_soc_ctrl_remove
> 
>     This commit has been introduced in v3 of the patchset.
> 
>     It includes a simplified version of common 'litex.h'
>     header introduced in v2 of the patchset.
> 
>  MAINTAINERS                        |   2 +
>  drivers/soc/Kconfig                |   1 +
>  drivers/soc/Makefile               |   1 +
>  drivers/soc/litex/Kconfig          |  14 ++
>  drivers/soc/litex/Makefile         |   3 +
>  drivers/soc/litex/litex_soc_ctrl.c | 217 +++++++++++++++++++++++++++++
>  include/linux/litex.h              |  45 ++++++
>  7 files changed, 283 insertions(+)
>  create mode 100644 drivers/soc/litex/Kconfig
>  create mode 100644 drivers/soc/litex/Makefile
>  create mode 100644 drivers/soc/litex/litex_soc_ctrl.c
>  create mode 100644 include/linux/litex.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 2f5ede8a08aa..a35be1be90d5 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -9729,6 +9729,8 @@ M:	Karol Gugala <kgugala@antmicro.com>
>  M:	Mateusz Holenko <mholenko@antmicro.com>
>  S:	Maintained
>  F:	Documentation/devicetree/bindings/*/litex,*.yaml
> +F:	drivers/soc/litex/litex_soc_ctrl.c
> +F:	include/linux/litex.h
>  
>  LIVE PATCHING
>  M:	Josh Poimboeuf <jpoimboe@redhat.com>
> diff --git a/drivers/soc/Kconfig b/drivers/soc/Kconfig
> index 1778f8c62861..78add2a163be 100644
> --- a/drivers/soc/Kconfig
> +++ b/drivers/soc/Kconfig
> @@ -9,6 +9,7 @@ source "drivers/soc/bcm/Kconfig"
>  source "drivers/soc/fsl/Kconfig"
>  source "drivers/soc/imx/Kconfig"
>  source "drivers/soc/ixp4xx/Kconfig"
> +source "drivers/soc/litex/Kconfig"
>  source "drivers/soc/mediatek/Kconfig"
>  source "drivers/soc/qcom/Kconfig"
>  source "drivers/soc/renesas/Kconfig"
> diff --git a/drivers/soc/Makefile b/drivers/soc/Makefile
> index 8b49d782a1ab..fd016b51cddd 100644
> --- a/drivers/soc/Makefile
> +++ b/drivers/soc/Makefile
> @@ -14,6 +14,7 @@ obj-$(CONFIG_ARCH_GEMINI)	+= gemini/
>  obj-$(CONFIG_ARCH_MXC)		+= imx/
>  obj-$(CONFIG_ARCH_IXP4XX)	+= ixp4xx/
>  obj-$(CONFIG_SOC_XWAY)		+= lantiq/
> +obj-$(CONFIG_LITEX_SOC_CONTROLLER) += litex/
>  obj-y				+= mediatek/
>  obj-y				+= amlogic/
>  obj-y				+= qcom/
> diff --git a/drivers/soc/litex/Kconfig b/drivers/soc/litex/Kconfig
> new file mode 100644
> index 000000000000..71264c0e1d6c
> --- /dev/null
> +++ b/drivers/soc/litex/Kconfig
> @@ -0,0 +1,14 @@
> +# SPDX-License_Identifier: GPL-2.0
> +
> +menu "Enable LiteX SoC Builder specific drivers"
> +
> +config LITEX_SOC_CONTROLLER
> +	tristate "Enable LiteX SoC Controller driver"
> +	help
> +	  This option enables the SoC Controller Driver which verifies
> +	  LiteX CSR access and provides common litex_get_reg/litex_set_reg
> +	  accessors.
> +	  All drivers that use functions from litex.h must depend on
> +	  LITEX_SOC_CONTROLLER.
> +
> +endmenu
> diff --git a/drivers/soc/litex/Makefile b/drivers/soc/litex/Makefile
> new file mode 100644
> index 000000000000..98ff7325b1c0
> --- /dev/null
> +++ b/drivers/soc/litex/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License_Identifier: GPL-2.0
> +
> +obj-$(CONFIG_LITEX_SOC_CONTROLLER)	+= litex_soc_ctrl.o
> diff --git a/drivers/soc/litex/litex_soc_ctrl.c b/drivers/soc/litex/litex_soc_ctrl.c
> new file mode 100644
> index 000000000000..5defba000fd4
> --- /dev/null
> +++ b/drivers/soc/litex/litex_soc_ctrl.c
> @@ -0,0 +1,217 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * LiteX SoC Controller Driver
> + *
> + * Copyright (C) 2020 Antmicro <www.antmicro.com>
> + *
> + */
> +
> +#include <linux/litex.h>
> +#include <linux/device.h>
> +#include <linux/errno.h>
> +#include <linux/of.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/printk.h>
> +#include <linux/module.h>
> +#include <linux/errno.h>
> +#include <linux/io.h>
> +
> +/*
> + * The parameters below are true for LiteX SoC
> + * configured for 8-bit CSR Bus, 32-bit aligned.
> + *
> + * Supporting other configurations will require
> + * extending the logic in this header.
> + */
> +#define LITEX_REG_SIZE             0x4
> +#define LITEX_SUBREG_SIZE          0x1
> +#define LITEX_SUBREG_SIZE_BIT      (LITEX_SUBREG_SIZE * 8)
> +
> +static DEFINE_SPINLOCK(csr_lock);
> +
> +static inline unsigned long read_pointer_with_barrier(
> +	const volatile void __iomem *addr)
> +{
> +	unsigned long val;
> +
> +	__io_br();
> +	val = *(const volatile unsigned long __force *)addr;
> +	__io_ar();
> +	return val;
> +}
This looks like an open-oced version of readl()
See include/asm-generic/io.h

> +
> +static inline void write_pointer_with_barrier(
> +	volatile void __iomem *addr, unsigned long val)
> +{
> +	__io_br();
> +	*(volatile unsigned long __force *)addr = val;
> +	__io_ar();
> +}
Likewise.

> +
> +/*
> + * 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/issues/314
> + *
> + * 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.
> + */
> +void litex_set_reg(
> +	void __iomem *reg, unsigned long reg_size, unsigned long val)
> +{

The typical linux style is:

void litex_set_reg(void __iomem *reg, unsigned long reg_size, unsigned long val)
{

And if the line is too long, then aling with tabs+spaces right after
first opening paranthese.

General comment for the remaining of the file.

> +	unsigned long shifted_data, shift, i;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&csr_lock, flags);
> +
> +	for (i = 0; i < reg_size; ++i) {
> +		shift = ((reg_size - i - 1) * LITEX_SUBREG_SIZE_BIT);
> +		shifted_data = val >> shift;
> +		write_pointer_with_barrier(
> +			reg + (LITEX_REG_SIZE * i), shifted_data);
> +	}
> +
> +	spin_unlock_irqrestore(&csr_lock, flags);
> +}
> +
> +unsigned long litex_get_reg(
> +	void __iomem *reg, unsigned long reg_size)
> +{
> +	unsigned long shifted_data, shift, i;
> +	unsigned long result = 0;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&csr_lock, flags);
> +
> +	for (i = 0; i < reg_size; ++i) {
> +		shifted_data = read_pointer_with_barrier(
> +			reg + (LITEX_REG_SIZE * i));
> +		shift = ((reg_size - i - 1) * LITEX_SUBREG_SIZE_BIT);
> +		result |= (shifted_data << shift);
> +	}
> +
> +	spin_unlock_irqrestore(&csr_lock, flags);
> +
> +	return result;
> +}
> +
> +static int accessors_ok;
> +
> +/*
> + * Check if accessors are safe to be used by other drivers
> + * returns true if yes - false if not
> + */
> +int litex_check_accessors(void)
> +{
> +	return accessors_ok;
> +}
> +
> +#define SCRATCH_REG_OFF         0x04
> +#define SCRATCH_REG_SIZE        4
> +#define SCRATCH_REG_VALUE       0x12345678
> +#define SCRATCH_TEST_VALUE      0xdeadbeef
> +
> +/*
> + * Check LiteX CSR read/write access
> + *
> + * This function reads and writes a scratch register in order
> + * to verify if CSR access works.
> + *
> + * In case any problems are detected, the driver should panic
> + * and not set `accessors_ok` flag. As a result no other
> + * LiteX driver should access CSR bus.
> + *
> + * Access to the LiteX CSR is, by design, done in CPU native
> + * endianness. The driver should not dynamically configure
> + * access functions when the endianness mismatch is detected.
> + * Such situation indicates problems in the soft SoC design
> + * and should be solved at the LiteX generator level,
> + * not in the software.
> + */
> +static int litex_check_csr_access(void __iomem *reg_addr)
> +{
> +	unsigned long reg;
> +
> +	reg = litex_get_reg(reg_addr + SCRATCH_REG_OFF, SCRATCH_REG_SIZE);
> +
> +	if (reg != SCRATCH_REG_VALUE) {
> +		panic("Scratch register read error! Expected: 0x%x but got: 0x%lx",
> +			SCRATCH_REG_VALUE, reg);
> +		return -EINVAL;
> +	}
> +
> +	litex_set_reg(reg_addr + SCRATCH_REG_OFF,
> +		SCRATCH_REG_SIZE, SCRATCH_TEST_VALUE);
> +	reg = litex_get_reg(reg_addr + SCRATCH_REG_OFF, SCRATCH_REG_SIZE);
> +
> +	if (reg != SCRATCH_TEST_VALUE) {
> +		panic("Scratch register write error! Expected: 0x%x but got: 0x%lx",
> +			SCRATCH_TEST_VALUE, reg);
> +		return -EINVAL;
> +	}
> +
> +	/* restore original value of the SCRATCH register */
> +	litex_set_reg(reg_addr + SCRATCH_REG_OFF,
> +		SCRATCH_REG_SIZE, SCRATCH_REG_VALUE);
> +
> +	/* Set flag for other drivers */
> +	accessors_ok = 1;
> +	pr_info("LiteX SoC Controller driver initialized");
> +
> +	return 0;
> +}
> +
> +struct litex_soc_ctrl_device {
> +	void __iomem *base;
> +};
> +
> +static const struct of_device_id litex_soc_ctrl_of_match[] = {
> +	{.compatible = "litex,soc-controller"},
> +	{},
> +};
> +
> +MODULE_DEVICE_TABLE(of, litex_soc_ctrl_of_match);
> +
> +static int litex_soc_ctrl_probe(struct platform_device *pdev)
> +{
> +	struct device *dev;
> +	struct device_node *node;
> +	struct litex_soc_ctrl_device *soc_ctrl_dev;
> +
> +	dev = &pdev->dev;
> +	node = dev->of_node;
> +	if (!node)
> +		return -ENODEV;
> +
> +	soc_ctrl_dev = devm_kzalloc(dev, sizeof(*soc_ctrl_dev), GFP_KERNEL);
> +	if (IS_ERR_OR_NULL(soc_ctrl_dev))
> +		return -ENOMEM;
devm_kzalloc() either return NULL or allocated memory.
No need to do IS_ERR_OR_NULL()

> +
> +	soc_ctrl_dev->base = devm_platform_ioremap_resource(pdev, 0);
> +	if (IS_ERR_OR_NULL(soc_ctrl_dev->base))
> +		return -EIO;
devm_platform_ioremap_resource does not return NUL on error.
So you loose the original error code here.

	Sam

> +
> +	return litex_check_csr_access(soc_ctrl_dev->base);
> +}
> +
> +static struct platform_driver litex_soc_ctrl_driver = {
> +	.driver = {
> +		.name = "litex-soc-controller",
> +		.of_match_table = of_match_ptr(litex_soc_ctrl_of_match)
> +	},
> +	.probe = litex_soc_ctrl_probe,
> +};
> +
> +module_platform_driver(litex_soc_ctrl_driver);
> +MODULE_DESCRIPTION("LiteX SoC Controller driver");
> +MODULE_AUTHOR("Antmicro <www.antmicro.com>");
> +MODULE_LICENSE("GPL v2");
> diff --git a/include/linux/litex.h b/include/linux/litex.h
> new file mode 100644
> index 000000000000..f31062436273
> --- /dev/null
> +++ b/include/linux/litex.h
> @@ -0,0 +1,45 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * 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>
> + */
> +
> +#ifndef _LINUX_LITEX_H
> +#define _LINUX_LITEX_H
> +
> +#include <linux/io.h>
> +#include <linux/types.h>
> +#include <linux/compiler_types.h>
> +
> +/*
> + * litex_check_accessors is a function implemented in
> + * drivers/soc/litex/litex_soc_controller.c
> + * checking if the common LiteX CSR accessors
> + * are safe to be used by the drivers;
> + * returns true (1) if yes - false (0) if not
> + *
> + * Important: All drivers that use litex_set_reg/litex_get_reg
> + * functions should make sure that LiteX SoC Controller driver
> + * has verified LiteX CSRs read and write operations before
> + * issuing any read/writes to the LiteX peripherals.
> + *
> + * Exemplary snippet that can be used at the beginning
> + * of the driver's probe() function to ensure that LiteX
> + * SoC Controller driver is properely initialized:
> + *
> + * if (!litex_check_accessors())
> + *     return -EPROBE_DEFER;
> + */
> +int litex_check_accessors(void);
> +
> +void litex_set_reg(void __iomem *reg, unsigned long reg_sz, unsigned long val);
> +
> +unsigned long litex_get_reg(void __iomem *reg, unsigned long reg_sz);
> +
> +
> +#endif /* _LINUX_LITEX_H */
> -- 
> 2.25.1