Re: [PATCH v2 05/11] xen/arm: Mark device as PCI while creating one

From: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: "julien@xen.org" <julien@xen.org>,
	"sstabellini@kernel.org" <sstabellini@kernel.org>,
	Oleksandr Tyshchenko <Oleksandr_Tyshchenko@epam.com>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>,
	Artem Mygaiev <Artem_Mygaiev@epam.com>,
	"roger.pau@citrix.com" <roger.pau@citrix.com>,
	Bertrand Marquis <bertrand.marquis@arm.com>,
	Rahul Singh <rahul.singh@arm.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>
Subject: Re: [PATCH v2 05/11] xen/arm: Mark device as PCI while creating one
Date: Tue, 28 Sep 2021 08:29:04 +0000	[thread overview]
Message-ID: <13b9cc76-c7e0-be7e-61d3-fc42a41dcc58@epam.com> (raw)
In-Reply-To: <31dc3429-b1f4-85ab-968d-c9054b77ac4f@suse.com>

On 28.09.21 11:26, Jan Beulich wrote:
> On 28.09.2021 10:09, Oleksandr Andrushchenko wrote:
>> On 27.09.21 13:26, Jan Beulich wrote:
>>> On 27.09.2021 12:04, Oleksandr Andrushchenko wrote:
>>>> On 27.09.21 13:00, Jan Beulich wrote:
>>>>> On 27.09.2021 11:35, Oleksandr Andrushchenko wrote:
>>>>>> On 27.09.21 12:19, Jan Beulich wrote:
>>>>>>> On 27.09.2021 10:45, Oleksandr Andrushchenko wrote:
>>>>>>>> On 27.09.21 10:45, Jan Beulich wrote:
>>>>>>>>> On 23.09.2021 14:54, Oleksandr Andrushchenko wrote:
>>>>>>>>>> --- a/xen/drivers/passthrough/pci.c
>>>>>>>>>> +++ b/xen/drivers/passthrough/pci.c
>>>>>>>>>> @@ -328,6 +328,9 @@ static struct pci_dev *alloc_pdev(struct pci_seg *pseg, u8 bus, u8 devfn)
>>>>>>>>>>           *((u8*) &pdev->bus) = bus;
>>>>>>>>>>           *((u8*) &pdev->devfn) = devfn;
>>>>>>>>>>           pdev->domain = NULL;
>>>>>>>>>> +#ifdef CONFIG_ARM
>>>>>>>>>> +    pci_to_dev(pdev)->type = DEV_PCI;
>>>>>>>>>> +#endif
>>>>>>>>> I have to admit that I'm not happy about new CONFIG_<arch> conditionals
>>>>>>>>> here. I'd prefer to see this done by a new arch helper, unless there are
>>>>>>>>> obstacles I'm overlooking.
>>>>>>>> Do you mean something like arch_pci_alloc_pdev(dev)?
>>>>>>> I'd recommend against "alloc" in its name; "new" instead maybe?
>>>>>> I am fine with arch_pci_new_pdev, but arch prefix points to the fact that
>>>>>> this is just an architecture specific part of the pdev allocation rather than
>>>>>> actual pdev allocation itself, so with this respect arch_pci_alloc_pdev seems
>>>>>> more natural to me.
>>>>> The bulk of the function is about populating the just allocated struct.
>>>>> There's no arch-specific part of the allocation (so far, leaving aside
>>>>> MSI-X), you only want and arch-specific part of the initialization. I
>>>>> would agree with "alloc" in the name if further allocation was to
>>>>> happen there.
>>>> Hm, then arch_pci_init_pdev sounds more reasonable
>>> Fine with me.
>> Do we want this to be void or returning an error code? If error code is needed,
>> then we would also need a roll-back function, e.g. arch_pci_free_pdev or
>> arch_pci_release_pdev or arch_pci_fini_pdev or something, so it can be used in
>> case of error or in free_pdev function.
> I'd start with void and make it return an error (and deal with necessary
> cleanup) only once a need arises.

Sounds reasonable. For x86 I think we can deal with:

xen/include/xen/pci.h:

#ifdef CONFIG_ARM
void arch_pci_init_pdev(struct pci_dev *pdev);
#else
static inline void arch_pci_init_pdev(struct pci_dev *pdev)
{
     return 0;
}
#endif

>
> Jan
>