linux-kernel - Re: [PATCH 04/24] PCI: Add busn

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Date:	Mon, 6 Feb 2012 12:45:15 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Tony Luck <tony.luck@...el.com>,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 04/24] PCI: Add busn_res operation functions

On Mon, Feb 6, 2012 at 10:59 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Sat, Feb 4, 2012 at 10:57 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>> will use them insert/update busn res in pci_bus
>>
>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>> ---
>>  drivers/pci/probe.c |   42 ++++++++++++++++++++++++++++++++++++++++++
>>  include/linux/pci.h |    3 +++
>>  2 files changed, 45 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>> index a114173..8d4de5e 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -1622,6 +1622,48 @@ err_out:
>>        return NULL;
>>  }
>>
>> +void pci_bus_insert_busn_res(struct pci_bus *b, int bus, int bus_max)
>> +{
>> +       struct resource *res = &b->busn_res;
>> +       struct resource *parent_res = &iobusn_resource;
>> +       int ret;
>> +
>> +       res->start = busn(pci_domain_nr(b), bus);
>> +       res->end = busn(pci_domain_nr(b), bus_max);
>> +       res->flags = IORESOURCE_BUS;
>> +
>> +       if (!pci_is_root_bus(b))
>> +               parent_res = &b->parent->busn_res;
>> +
>> +       ret = insert_resource(parent_res, res);
>> +
>> +       dev_printk(KERN_DEBUG, &b->dev,
>> +                       "busn_res: %pR %s inserted under %pR\n",
>> +                       res, ret ? "can not be" : "is", parent_res);
>> +}
>> +
>> +void pci_bus_update_busn_res_end(struct pci_bus *b, int bus_max)
>> +{
>> +       struct resource *res = &b->busn_res;
>> +       struct resource old_res = *res;
>> +
>> +       res->end = busn_update_bus_nr(res->end, bus_max);
>
> I think this design is a mistake.  Here's what you're doing:
>
>  - initialize struct resource (keys are "start" and "end")
>  - insert into tree (placed in tree by kernel/resource.c based on
> "start" and "end")
>  - update "end"
>
> You "know" in this case that the update is safe because the caller has
> validated "bus_max."  But that still breaks the kernel/resource.c
> encapsulation.  If we change the kernel/resource.c implementation,
> this code might break.

the point is: I only want to reuse allocate_resource() to get right position.
and the code does not depends to kernel/resource.c much.

>
> I think it would be better to remove the bus resource from the tree,
> change its "end," then re-insert it.

how about parent buses that have extended top?

Yinghai
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