From: John Garry <john.garry@huawei.com>
To: Niklas Schnelle <schnelle@linux.ibm.com>,
Bjorn Helgaas <helgaas@kernel.org>,
Mauro Carvalho Chehab <mchehab@kernel.org>,
"Arnd Bergmann" <arnd@arndb.de>
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Subject: Re: [RFC 01/32] Kconfig: introduce and depend on LEGACY_PCI
Date: Wed, 5 Jan 2022 17:42:16 +0000 [thread overview]
Message-ID: <3f39d8a2-2e57-a671-2926-eb4f2bf20c76@huawei.com> (raw)
In-Reply-To: <e0877e91d7d50299ea5a3ffcee2cf1016458ce10.camel@linux.ibm.com>
On 29/12/2021 16:55, Niklas Schnelle wrote:
> On Wed, 2021-12-29 at 10:03 -0600, Bjorn Helgaas wrote:
>> On Wed, Dec 29, 2021 at 01:12:07PM +0100, Mauro Carvalho Chehab wrote:
>>> Em Wed, 29 Dec 2021 12:45:38 +0100
>>> Niklas Schnelle<schnelle@linux.ibm.com> escreveu:
>>>> ...
>>>> I do think we agree that once done correctly there is value in
>>>> such an option independent of HAS_IOPORT only gating inb() etc uses.
>> I'm not sure I'm convinced about this. For s390, you could do this
>> patch series, where you don't define inb() at all, and you add new
>> dependencies to prevent compile errors. Or you could define inb() to
>> return ~0, which is what happens on other platforms when the device is
>> not present.
>>
>>> Personally, I don't see much value on a Kconfig var for legacy PCI I/O
>>> space. From maintenance PoV, bots won't be triggered if someone use
>>> HAS_IOPORT instead of the PCI specific one - or vice-versa. So, we
>>> could end having a mix of both at the wrong places, in long term.
>>>
>>> Also, assuming that PCIe hardware will some day abandon support for
>>> "legacy" PCI I/O space, I guess some runtime logic would be needed,
>>> in order to work with both kinds of PCIe controllers. So, having a
>>> Kconfig option won't help much, IMO.
>>>
>>> So, my personal preference would be to have just one Kconfig var, but
>>> I'm ok if the PCI maintainers decide otherwise.
>> I don't really like the "LEGACY_PCI" Kconfig option. "Legacy" just
>> means something old and out of favor; it doesn't say*what* that
>> something is.
>>
>> I think you're specifically interested in I/O port space usage, and it
>> seems that you want all PCI drivers that*only* use I/O port space to
>> depend on LEGACY_PCI? Drivers that can use either I/O or memory
>> space or both would not depend on LEGACY_PCI? This seems a little
>> murky and error-prone.
> I'd like to hear Arnd's opinion on this but you're the PCI maintainer
> so of course your buy-in would be quite important for such an option.
>
Hi Niklas,
I can't see the value in the LEGACY_PCI config - however I don't really
understand Arnd's original intention.
It was written that it would allow us to control "whether we have any
pre-PCIe devices or those PCIe drivers that need PIO accessors other
than ioport_map()/pci_iomap()".
However I just don't see why CONFIG_PCI=y and CONFIG_HAS_IOPORT=y aren't
always the gating factor here. Arnd?
Thanks,
John
next prev parent reply other threads:[~2022-01-06 8:24 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20211227164317.4146918-1-schnelle@linux.ibm.com>
2021-12-27 16:42 ` [RFC 01/32] Kconfig: introduce and depend on LEGACY_PCI Niklas Schnelle
2021-12-27 17:48 ` Guenter Roeck
2021-12-28 2:09 ` Mauro Carvalho Chehab
2021-12-28 8:21 ` Greg Kroah-Hartman
2021-12-28 9:15 ` Mauro Carvalho Chehab
2021-12-28 10:58 ` Niklas Schnelle
2021-12-28 12:01 ` Greg Kroah-Hartman
2021-12-28 12:54 ` Mauro Carvalho Chehab
2021-12-28 15:06 ` Niklas Schnelle
2021-12-28 17:12 ` Mauro Carvalho Chehab
2021-12-29 11:45 ` Niklas Schnelle
2021-12-29 12:12 ` Mauro Carvalho Chehab
2021-12-29 16:03 ` Bjorn Helgaas
2021-12-29 16:55 ` Niklas Schnelle
2022-01-05 17:42 ` John Garry [this message]
2022-01-05 19:47 ` Bjorn Helgaas
[not found] ` <74bf4fde-3972-1c36-ca04-58089da0d82b@huawei.com>
2022-01-06 18:14 ` Bjorn Helgaas
2022-01-07 17:16 ` John Garry
2022-01-10 9:34 ` Niklas Schnelle
2021-12-27 16:43 ` [RFC 22/32] video: handle HAS_IOPORT dependencies Niklas Schnelle
2021-12-27 16:43 ` [RFC 26/32] drm: " Niklas Schnelle
2022-01-03 6:11 ` Gerd Hoffmann
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