linux-kernel - Re: [PATCH] p2sb: Don't init until unassigned resources have been assigned.

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Date: Thu, 9 May 2024 19:04:32 +0200
From: Lukas Wunner <lukas@...ner.de>
To: bcfradella@...ton.me, Shinichiro Kawasaki <shinichiro.kawasaki@....com>,
	Klara Modin <klarasmodin@...il.com>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Danil Rybakov <danilrybakov249@...il.com>
Cc: Hans de Goede <hdegoede@...hat.com>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ben Fradella <bfradell@...app.com>,
	Ranjan Dutta <ranjan.dutta@...el.com>,
	Yifan2 Li <yifan2.li@...el.com>,
	Jonathan Yong <jonathan.yong@...el.com>
Subject: Re: [PATCH] p2sb: Don't init until unassigned resources have been
 assigned.

[cc += Shin'ichiro, Klara, Andy, Danil]

On Thu, May 09, 2024 at 04:49:34PM +0000, bcfradella@...ton.me wrote:
> From: Ben Fradella <bfradell@...app.com>
> 
> The P2SB could get an invalid BAR from the BIOS, and that won't be fixed
> up until pcibios_assign_resources(), which is an fs_initcall().
> 
> - Move p2sb_fs_init() to an fs_initcall_sync(). This is still early
>   enough to avoid a race with any dependent drivers.
> 
> - Add a check for IORESOURCE_UNSET in p2sb_valid_resource() to catch
>   unset BARs going forward.
> 
> - Return error values from p2sb_fs_init() so that the 'initcall_debug'
>   cmdline arg provides useful data.
> 
> Signed-off-by: Ben Fradella <bfradell@...app.com>
> ---
>  drivers/platform/x86/p2sb.c | 29 +++++++++++++++--------------
>  1 file changed, 15 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/platform/x86/p2sb.c b/drivers/platform/x86/p2sb.c
> index 3d66e1d4eb1f..1938a3ef9480 100644
> --- a/drivers/platform/x86/p2sb.c
> +++ b/drivers/platform/x86/p2sb.c
> @@ -56,12 +56,9 @@ static int p2sb_get_devfn(unsigned int *devfn)
>  	return 0;
>  }
>  
> -static bool p2sb_valid_resource(struct resource *res)
> +static bool p2sb_valid_resource(const struct resource *res)
>  {
> -	if (res->flags)
> -		return true;
> -
> -	return false;
> +	return res->flags & ~IORESOURCE_UNSET;
>  }
>  
>  /* Copy resource from the first BAR of the device in question */
> @@ -220,16 +217,20 @@ EXPORT_SYMBOL_GPL(p2sb_bar);
>  
>  static int __init p2sb_fs_init(void)
>  {
> -	p2sb_cache_resources();
> -	return 0;
> +	return p2sb_cache_resources();
>  }
>  
>  /*
> - * pci_rescan_remove_lock to avoid access to unhidden P2SB devices can
> - * not be locked in sysfs pci bus rescan path because of deadlock. To
> - * avoid the deadlock, access to P2SB devices with the lock at an early
> - * step in kernel initialization and cache required resources. This
> - * should happen after subsys_initcall which initializes PCI subsystem
> - * and before device_initcall which requires P2SB resources.
> + * pci_rescan_remove_lock() can not be locked in sysfs pci bus rescan path
> + * because of deadlock. To avoid the deadlock, access P2SB devices with the lock
> + * at an early step in kernel initialization and cache required resources.
> + *
> + * We want to run as early as possible. If the P2SB was assigned a bad BAR,
> + * we'll need to wait on pcibios_assign_resources() to fix it. So, our list of
> + * initcall dependencies looks something like this:
> + *
> + * ...
> + * subsys_initcall (pci_subsys_init)
> + * fs_initcall     (pcibios_assign_resources)
>   */
> -fs_initcall(p2sb_fs_init);
> +fs_initcall_sync(p2sb_fs_init);
> -- 
> 2.43.0