linux-kernel - Re: [PATCH v3 3/6] PCI: generic: Quit clobbering our pci

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Date:	Wed, 23 Sep 2015 08:56:59 -0700
From:	David Daney <ddaney@...iumnetworks.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-arm-kernel@...ts.infradead.org>,
	David Daney <ddaney.cavm@...il.com>,
	<linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	<linux-pci@...r.kernel.org>, Will Deacon <will.deacon@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	<devicetree@...r.kernel.org>, Marc Zyngier <marc.zyngier@....com>,
	"David Daney" <david.daney@...ium.com>
Subject: Re: [PATCH v3 3/6] PCI: generic: Quit clobbering our pci_ops.

On 09/23/2015 01:21 AM, Arnd Bergmann wrote:
> On Tuesday 22 September 2015 16:49:14 David Daney wrote:
>> From: David Daney <david.daney@...ium.com>
>>
>> The pci-host-generic driver keeps a global struct pci_ops which it
>> then patches with the .map_bus method appropriate for the bus device.
>> A problem arises when the driver is used for two different types of
>> bus devices, the .map_bus method for the last device probed clobbers
>> the method for all previous devices.  The result, only the last bus
>> device probed has the proper .map_bus, and the others fail.
>>
>> Move the struct pci_ops into the bus specific structure, and
>> initialize it when the bus device is probed.  Keep a copy of the
>> gen_pci_cfg_bus_ops structure, instead of a pointer to a global copy,
>
> This is a very useful change.
>
>> to future proof against the addition of bus specific elements to
>> struct pci_ops.
>
> but I don't like this part. We should just not have bus specific
> elements in pci_ops. We don't really have that here either, except
> that the gen_pci driver had a hack for reusing the same operations
> for things that are actually different.
>
> It's an established practice that anything named '*_operations' is
> meant to be constant and ideally defined as 'static const ... *_ops;'
> in the driver. We could try to enforce this better by marking
> bus->ops as 'const' and changing all the instances of this structure
> accordingly.
>
>> @@ -65,7 +65,11 @@ static void __iomem *gen_pci_map_cfg_bus_cam(struct pci_bus *bus,
>>
>>   static struct gen_pci_cfg_bus_ops gen_pci_cfg_cam_bus_ops = {
>>   	.bus_shift	= 16,
>> -	.map_bus	= gen_pci_map_cfg_bus_cam,
>> +	.ops		= {
>> +		.map_bus	= gen_pci_map_cfg_bus_cam,
>> +		.read		= pci_generic_config_read,
>> +		.write		= pci_generic_config_write,
>> +	}
>>   };
>
> So this is good. We could in theory unify the map_bus functions
> like this now:
>
> static void __iomem *gen_pci_map_cfg_bus(struct pci_bus *bus,
>                                           unsigned int devfn,
>                                           int where)
> {
>          struct gen_pci *pci = bus->sysdata;
> 	struct gen_pci_cfg_bus_ops *ops;
>          resource_size_t idx;
>
> 	ops = container_of(bus->ops, struct gen_pci_cfg_bus_ops, ops);
> 	idx = bus->number - pci->cfg.bus_range->start;
>
>          return pci->cfg.win[idx] + ((devfn << ops->dev_shift) | where);
> }
>
> Not sure if that improves clarity or not, up to Will.
>
>> @@ -234,8 +237,7 @@ static int gen_pci_probe(struct platform_device *pdev)
>>   	}
>>
>>   	of_id = of_match_node(gen_pci_of_match, np);
>> -	pci->cfg.ops = of_id->data;
>> +	pci->cfg.ops = *(struct gen_pci_cfg_bus_ops *)of_id->data;
>
> This is the part that grabbed my attention, we should not do it like this.
>

I will consider changing this so that a structure copy is not used, 
perhaps as you suggest above.

David Daney.


> 	Arnd
>

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