linux-kernel - Re: [PATCH 4/7] coresight: tpiu: Move ACPI support from AMBA driver to platform driver

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Message-ID: <268e1605-fe3f-4aa0-92e3-36ddfc8aacb3@arm.com>
Date:   Wed, 22 Nov 2023 12:32:33 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     James Clark <james.clark@....com>,
        linux-arm-kernel@...ts.infradead.org, suzuki.poulose@....com
Cc:     Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH 4/7] coresight: tpiu: Move ACPI support from AMBA driver
 to platform driver



On 11/15/23 19:23, James Clark wrote:
> 
> 
> On 27/10/2023 08:29, Anshuman Khandual wrote:
>> Add support for the tpiu device in the platform driver, which can then be
>> used on ACPI based platforms. This change would now allow runtime power
>> management for ACPI based systems. The driver would try to enable the APB
>> clock if available.
>>
> [...]
>> +#ifdef CONFIG_ACPI
>> +static const struct acpi_device_id tpiu_acpi_ids[] = {
>> +	{"ARMHC979", 0}, /* ARM CoreSight TPIU */
>> +	{}
>> +};
>> +MODULE_DEVICE_TABLE(acpi, tpiu_acpi_ids);
>> +#endif
>> +
>> +static struct platform_driver tpiu_platform_driver = {
>> +	.probe	= tpiu_platform_probe,
>> +	.remove	= tpiu_platform_remove,
>> +	.driver = {
>> +		.name			= "coresight-tpiu-platform",
>> +		.acpi_match_table	= ACPI_PTR(tpiu_acpi_ids),
>> +		.suppress_bind_attrs	= true,
>> +		.pm			= &tpiu_dev_pm_ops,
>> +	},
>> +};
>> +module_platform_driver(tpiu_platform_driver);
>> +
> 
> Is there a special build config where this works? I get an error here

I have been testing this with a config known to work on RB5 board.

> because module_platform_driver() redefines things that are in
> module_amba_driver() which is defined above:
> 
>   module_amba_driver(tpiu_driver);
> 
> This isn't a W=1 build or anything, just a normal one. And it applies to
> most of the patches in this set.

You are right, I am able to recreate this problem with defconfig on
6.7-rc2 as well. The problem here seems to be caused by having both
module_amba_driver() and module_platform_driver() in the same file.

#define module_amba_driver(__amba_drv) \
        module_driver(__amba_drv, amba_driver_register, amba_driver_unregister)

#define module_platform_driver(__platform_driver) \
        module_driver(__platform_driver, platform_driver_register, \
                        platform_driver_unregister)

Although, AFAICT, have not seen these before - even on the defconfig.
Just to work around this problem, there can be a common module_init()
/module_exit() to register/unregister both AMBA and platform drivers,
similar to etm4x_init()/etm4x_exit() setup in coresight-etm4x-core.c.