linux-kernel - Re: [PATCH] VFIO: platform: AMD xgbe reset module

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Date:	Fri, 16 Oct 2015 15:56:03 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, eric.auger@...com,
	b.reynal@...tualopensystems.com, kvmarm@...ts.cs.columbia.edu,
	kvm@...r.kernel.org, thomas.lendacky@....com, patches@...aro.org,
	suravee.suthikulpanit@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] VFIO: platform: AMD xgbe reset module

Hi Arnd,
On 10/16/2015 03:26 PM, Arnd Bergmann wrote:
> On Friday 16 October 2015 15:06:45 Eric Auger wrote:
> 
>>  I've since forgotten his answer, but the fact that
>>> __symbol_get() is only defined for modules makes it moot, we either need
>>> to make symbol_get() work or define __symbol_get() for non-module
>>> builds.
>> I currently don't see any solution for any of those. The only solution I
>> can see is someone registers the reset function pointer to vfio.
>>
>> I think we could keep the existing reset modules, do the request_module
>> from VFIO, using their module name registered in the lookup table. But
>> instead of having the reset function in the look-up table we would have
>> the reset modules register their reset function pointer to VFIO. I think
>> this could work around the symbol_get issue.
>>
>> This still leaves the layer violation argument though.
>>
>> Assuming this works, would that be an acceptable solution, although I
>> acknowledge this does not perfectly fit into the driver model?
> 
> I think it's possible to avoid the layering violation that way too,
> by loading the module based on the compatible string, with a module_alias.
> 
> static void vfio_platform_get_reset(struct vfio_platform_device *vdev,
>                                     struct device *dev)
> {
>         const char *compat;
>         int (*reset)(struct vfio_platform_device *);
>         int ret, i;
> 	char modname[256];
> 
>         ret = device_property_read_string(dev, "compatible", &compat);
>         if (ret)
>                 return;
> 
> 	reset = vfio_platform_lookup_reset(compat);
> 	if (!reset) {
> 		snprintf(modname, "vfio-reset:%s", compat);
> 		request_module(modname);
> 		reset = vfio_platform_lookup_reset(compat);
> 	}
> 
> 	vdev->reset = reset;
> }
> 
> ---
> 
> #define module_vfio_reset_handler(compat, reset)			\
> MODULE_ALIAS("vfio_reset" compat);					\
> static int reset ## _module_init(void)					\
> {									\
> 	return vfio_reset_register(THIS_MODULE, compat, &reset);	\
> }
> 
> I think that solution is good enough, as it avoids most of the
> problems with the current implementation but is a simple enough change.

That looks a good perspective. Thanks for the hint! Let's code now ;-)

Best Regards

Eric


> 
> 	Arnd
> 

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