RE: [PATCH v9 3/5] EINJ: Migrate to a platform driver

[Dan Williams <dan.j.williams@intel.com>]

Ben Cheatham wrote:
> Change the EINJ module to install a platform device/driver on module
> init and move the module init() and exit() functions to driver probe and
> remove. This change allows the EINJ module to load regardless of whether
> setting up EINJ succeeds, which allows dependent modules to still load
> (i.e. the CXL core).
> 
> Since EINJ may no longer be initialized when the module loads, any
> functions that are called from dependent/external modules should check
> the einj_initialized variable before calling any EINJ functions.
> 
> Signed-off-by: Ben Cheatham <Benjamin.Cheatham@amd.com>
> ---
>  drivers/acpi/apei/einj.c | 43 ++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 41 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/apei/einj.c b/drivers/acpi/apei/einj.c
> index 013eb621dc92..10d51cd73fa4 100644
> --- a/drivers/acpi/apei/einj.c
> +++ b/drivers/acpi/apei/einj.c
> @@ -21,6 +21,7 @@
>  #include <linux/nmi.h>
>  #include <linux/delay.h>
>  #include <linux/mm.h>
> +#include <linux/platform_device.h>
>  #include <asm/unaligned.h>
>  
>  #include "apei-internal.h"
> @@ -136,6 +137,12 @@ static struct apei_exec_ins_type einj_ins_type[] = {
>   */
>  static DEFINE_MUTEX(einj_mutex);
>  
> +/*
> + * Functions called from dependent modules should check this variable
> + * before using any EINJ functionality.
> + */

This reads slightly odd to me, is this clearer?

"Exported APIs use this flag to exit early if einj_probe() failed."

> +static bool einj_initialized;

This can be marked __ro_after_init to make it clear that it is static
for the lifetime of the module.

> +
>  static void *einj_param;
>  
>  static void einj_exec_ctx_init(struct apei_exec_context *ctx)
> @@ -684,7 +691,7 @@ static int einj_check_table(struct acpi_table_einj *einj_tab)
>  	return 0;
>  }
>  
> -static int __init einj_init(void)
> +static int einj_probe(struct platform_device *pdev)

This can remain __init since nothing will call this function port
init().

>  {
>  	int rc;
>  	acpi_status status;
> @@ -782,7 +789,7 @@ static int __init einj_init(void)
>  	return rc;
>  }
>  
> -static void __exit einj_exit(void)
> +static void einj_remove(struct platform_device *pdev)

Similarly this can remain __exit.
 
>  {
>  	struct apei_exec_context ctx;
>  
> @@ -801,6 +808,38 @@ static void __exit einj_exit(void)
>  	acpi_put_table((struct acpi_table_header *)einj_tab);
>  }
>  
> +static struct platform_device *einj_dev;
> +struct platform_driver einj_driver = {
> +	.remove_new = einj_remove,
> +	.driver = {
> +		.name = "einj",

Perhaps call this acpi-einj just to preserve the namespace in case a
cross-platform generic "einj" comes along.

> +	},
> +};
> +
> +static int __init einj_init(void)
> +{
> +	struct platform_device_info einj_dev_info = {
> +		.name = "einj",

Ditt "acpi-einj"

> +		.id = -1,
> +	};
> +
> +	einj_dev = platform_device_register_full(&einj_dev_info);

Just return early here if this failed.

> +	einj_initialized = !platform_driver_probe(&einj_driver, einj_probe);

Nit, but since platform_driver_probe() does not return bool, I would
prefer this to be more explicit:

	err = platform_driver_probe();
	einj_initialized = err == 0;

I think it is ok for the platform-device to stick around if einj_probe()
failures as userspace can see that the module is loaded but driver-init
failed.

Similarly it's probably also ok to fail the module load if
platform_device_register_full() fails since something deeper is wrong
with the system if it is starting to fail something so basic.

> +	if (!(einj_initialized || IS_ERR_OR_NULL(einj_dev)))
> +		platform_device_del(einj_dev);
> +
> +	return 0;
> +}
> +
> +static void __exit einj_exit(void)
> +{
> +	if (einj_initialized) {
> +		platform_driver_unregister(&einj_driver);
> +		platform_device_del(einj_dev);

Per above, this device_del can move outside the conditional.