Re: [PATCH v5 2/3] firmware: add Exynos ACPM protocol driver

[Tudor Ambarus <tudor.ambarus@linaro.org>]

Hi, Krzysztof,

On 12/31/24 2:32 PM, Tudor Ambarus wrote:
>>> diff --git a/drivers/firmware/samsung/Kconfig b/drivers/firmware/samsung/Kconfig
>>> new file mode 100644
>>> index 000000000000..750b41342174
>>> --- /dev/null
>>> +++ b/drivers/firmware/samsung/Kconfig
>>> @@ -0,0 +1,14 @@
>>> +# SPDX-License-Identifier: GPL-2.0-only
>>> +
>>> +config EXYNOS_ACPM_PROTOCOL
>>> +	tristate "Exynos Alive Clock and Power Manager (ACPM) Message Protocol"
>>> +	depends on ARCH_EXYNOS || COMPILE_TEST
>>> +	depends on EXYNOS_MBOX
>>
>> Is it build time dependency? No || COMPILE_TEST?
> 
> There's no build time dependency, I'll drop this line.
>>
>> Is it fine when EXYNOS_MBOX is a module?
> 
> Yes. When the EXYNOS_MBOX module is not loaded, and one tries to load
> EXYNOS_ACPM_PROTOCOL module, the later will defer probe when requesting
> the mailbox channels, but that's fine.
> 

I'll need to select EXYNOS_MBOX, I explain why below.

cut

>>> + */
>>> +static const struct acpm_handle *acpm_get_by_phandle(struct device_node *np,
>>> +						     const char *property)
>>> +{
>>> +	struct acpm_handle *handle = NULL;
>>> +	struct device_node *acpm_np;
>>> +	struct acpm_info *info;
>>> +
>>> +	if (!np) {
>>> +		pr_err("I need a device pointer\n");
>>> +		return ERR_PTR(-EINVAL);
>>> +	}
>>> +
>>> +	acpm_np = of_parse_phandle(np, property, 0);
>>> +	if (!acpm_np)
>>> +		return ERR_PTR(-ENODEV);
>>> +
>>> +	mutex_lock(&acpm_list_mutex);
>>> +	list_for_each_entry(info, &acpm_list, node) {
>>> +		if (acpm_np == info->dev->of_node) {
>>> +			handle = &info->handle;
>>> +			info->users++;
>>> +			break;
>>> +		}
>>> +	}
>>> +	mutex_unlock(&acpm_list_mutex);
>>> +	of_node_put(acpm_np);
>>> +
>>
>> You also need device links and probably try_module_get. See clk.c

I find these necessary too, will add them. try_module_get() must be
called when the module exists and is alive, otherwise I get a NULL ptr
dereference. I need a module dependency between acpm-protocol.ko and
exynos-mailbox.ko.
	select EXYNOS_MBOX and
	MODULE_SOFTDEP("pre: exynos-mailbox");
shall do the trick I think.

>> clk_hw_create_clk() or of_qcom_ice_get(). Interestingly, none of them
>> perform both operations, which I think is necessary.
>>
>> I think you could also avoid entire list and mutex by using
>> platform_get_drvdata(), see of_qcom_ice_get().

Using platform_get_drvdata() will simplify the code, thanks. It still
assumes the platform driver exists and is alive, otherwise we get a NULL
ptr dereference when getting the drvdata. But we'll be safe if I add the
module dependency.

Thanks,
ta