Re: [PATCH v3 4/6] bus: stm32_sys_bus: add support for STM32MP15 and STM32MP13 system bus

[Gatien CHEVALLIER <gatien.chevallier@foss.st.com>]

Hi Jonathan,

On 1/28/23 17:12, Jonathan Cameron wrote:
> On Fri, 27 Jan 2023 17:40:38 +0100
> Gatien Chevallier <gatien.chevallier@foss.st.com> wrote:
> 
>> This driver is checking the access rights of the different
>> peripherals connected to the system bus. If access is denied,
>> the associated device tree node is skipped so the platform bus
>> does not probe it.
>>
>> Signed-off-by: Gatien Chevallier <gatien.chevallier@foss.st.com>
>> Signed-off-by: Loic PALLARDY <loic.pallardy@st.com>
> 
> Hi Gatien,
> 
> A few comments inline,
> 
> Thanks,
> 
> Jonathan
> 
>> diff --git a/drivers/bus/stm32_sys_bus.c b/drivers/bus/stm32_sys_bus.c
>> new file mode 100644
>> index 000000000000..c12926466bae
>> --- /dev/null
>> +++ b/drivers/bus/stm32_sys_bus.c
>> @@ -0,0 +1,168 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (C) 2023, STMicroelectronics - All Rights Reserved
>> + */
>> +
>> +#include <linux/bitfield.h>
>> +#include <linux/bits.h>
>> +#include <linux/device.h>
>> +#include <linux/err.h>
>> +#include <linux/io.h>
>> +#include <linux/init.h>
>> +#include <linux/kernel.h>
>> +#include <linux/module.h>
>> +#include <linux/of.h>
>> +#include <linux/of_platform.h>
>> +#include <linux/platform_device.h>
>> +
>> +/* ETZPC peripheral as firewall bus */
>> +/* ETZPC registers */
>> +#define ETZPC_DECPROT			0x10
>> +
>> +/* ETZPC miscellaneous */
>> +#define ETZPC_PROT_MASK			GENMASK(1, 0)
>> +#define ETZPC_PROT_A7NS			0x3
>> +#define ETZPC_DECPROT_SHIFT		1
> 
> This define makes the code harder to read.  What we care about is
> the number of bits in the register divided by number of entries.
> (which is 2) hence the shift by 1. See below for more on this.
> 
> 
>> +
>> +#define IDS_PER_DECPROT_REGS		16
> 
>> +#define STM32MP15_ETZPC_ENTRIES		96
>> +#define STM32MP13_ETZPC_ENTRIES		64
> 
> These defines just make the code harder to check.
> They aren't magic numbers, but rather just telling us how many
> entries there are, so I would just put them in the structures directly.
> Their use make it clear what they are without needing to give them a name.
> 

Honestly, I'd rather read the hardware configuration registers to get 
this information instead of differentiating MP13/15. Would you agree on 
that?

> 
>> +struct stm32_sys_bus_match_data {
> 
> Comment on naming of this below.
> 
>> +	unsigned int max_entries;
>> +};
>> +
> 
> +static int stm32_etzpc_get_access(struct sys_bus_data *pdata, struct device_node *np)
> +{
> +	int err;
> +	u32 offset, reg_offset, sec_val, id;
> +
> +	err = stm32_sys_bus_get_periph_id(pdata, np, &id);
> +	if (err)
> +		return err;
> +
> +	/* Check access configuration, 16 peripherals per register */
> +	reg_offset = ETZPC_DECPROT + 0x4 * (id / IDS_PER_DECPROT_REGS);
> +	offset = (id % IDS_PER_DECPROT_REGS) << ETZPC_DECPROT_SHIFT;
> 
> Use of defines in here is actively unhelpful when it comes to review. I would suggest letting
> the maths be self explanatory (even if it's more code).
> 
> 	offset = (id % IDS_PER_DECPROT_REGS) * (sizeof(u32) * BITS_PER_BYTE / IDS_PER_DECPROT_REGS);
> 
> Or if you prefer have a define of
> 
> #define DECPROT_BITS_PER_ID (sizeof(u32) * BITS_PER_BYTE / IDS_PER_DECPROT_REGS)
> 
> and
> 	offset = (id % IDS_PER_DECPROT_REGS) * DECPROT_BITS_PER_ID;
> 

Ok I'll rework this for better understanding. Your suggestion seems fine

> +
> +	/* Verify peripheral is non-secure and attributed to cortex A7 */
> +	sec_val = (readl(pdata->sys_bus_base + reg_offset) >> offset) & ETZPC_PROT_MASK;
> +	if (sec_val != ETZPC_PROT_A7NS) {
> +		dev_dbg(pdata->dev, "Invalid bus configuration: reg_offset %#x, value %d\n",
> +			reg_offset, sec_val);
> +		return -EACCES;
> +	}
> +
> +	return 0;
> +}
> +
> ...
> 
>> +static int stm32_sys_bus_probe(struct platform_device *pdev)
>> +{
>> +	struct sys_bus_data *pdata;
>> +	void __iomem *mmio;
>> +	struct device_node *np = pdev->dev.of_node;
> 
> I'd be consistent. You use dev_of_node() accessor elsewhere, so should
> use it here as well >> +
>> +	pdata = devm_kzalloc(&pdev->dev, sizeof(*pdata), GFP_KERNEL);
>> +	if (!pdata)
>> +		return -ENOMEM;
>> +
>> +	mmio = devm_platform_ioremap_resource(pdev, 0);
>> +	if (IS_ERR(mmio))
>> +		return PTR_ERR(mmio);
>> +
>> +	pdata->sys_bus_base = mmio;
>> +	pdata->pconf = of_device_get_match_data(&pdev->dev);
>> +	pdata->dev = &pdev->dev;
>> +
>> +	platform_set_drvdata(pdev, pdata);
> 
> Does this get used? I can't immediately spot where but maybe I just
> missed it.
> 

Not for now :)

>> +
>> +	stm32_sys_bus_populate(pdata);
>> +
>> +	/* Populate all available nodes */
>> +	return of_platform_populate(np, NULL, NULL, &pdev->dev);
> 
> As np only used here, I'd not bother with the local variable in this function.
> 

Agreed

>> +}
>> +
>> +static const struct stm32_sys_bus_match_data stm32mp15_sys_bus_data = {
> 
> Naming a structure after where it comes from is a little unusual and
> confusion when a given call gets it from somewhere else.
> 
> I'd expect it to be named after what sort of thing it contains.
> stm32_sys_bus_info or something like that.
> 

Then, this shall be removed thanks to the read to hardware registers.

>> +	.max_entries = STM32MP15_ETZPC_ENTRIES,
>> +};
>> +
>> +static const struct stm32_sys_bus_match_data stm32mp13_sys_bus_data = {
>> +	.max_entries = STM32MP13_ETZPC_ENTRIES,
>> +};
>> +
>> +static const struct of_device_id stm32_sys_bus_of_match[] = {
>> +	{ .compatible = "st,stm32mp15-sys-bus", .data = &stm32mp15_sys_bus_data },
>> +	{ .compatible = "st,stm32mp13-sys-bus", .data = &stm32mp13_sys_bus_data },
> 
> Alphabetical order usually preferred when there isn't a strong reason for
> another choice.
> 

I second that

>> +	{}
>> +};
>> +MODULE_DEVICE_TABLE(of, stm32_sys_bus_of_match);
>> +
>> +static struct platform_driver stm32_sys_bus_driver = {
>> +	.probe  = stm32_sys_bus_probe,
>> +	.driver = {
>> +		.name = "stm32-sys-bus",
>> +		.of_match_table = stm32_sys_bus_of_match,
>> +	},
>> +};
>> +
>> +static int __init stm32_sys_bus_init(void)
>> +{
>> +	return platform_driver_register(&stm32_sys_bus_driver);
>> +}
>> +arch_initcall(stm32_sys_bus_init);
>> +
> 
> Unwanted trailing blank line.
> 

Good spot, thanks

> 

Best regards,
Gatien