[PATCH 7/8] PCI: Skip bridge window reads when window is not supported

[Caleb James DeLisle]

On 03/03/2026 22:23, Bjorn Helgaas wrote:
> On Tue, Mar 03, 2026 at 07:09:47PM +0000, Caleb James DeLisle wrote:
>> pci_read_bridge_io() and pci_read_bridge_mmio_pref() read bridge window
>> registers unconditionally. If the registers are hardwired to zero
>> (not implemented), both base and limit will be 0. Since (0 <= 0) is
>> true, a bogus window [mem 0x00000000-0x000fffff] or [io 0x0000-0x0fff]
>> gets created.
>>
>> pci_read_bridge_windows() already detects unsupported windows by
>> testing register writability and sets io_window/pref_window flags
>> accordingly. Check these flags at the start of pci_read_bridge_io()
>> and pci_read_bridge_mmio_pref() to skip reading registers when the
>> window is not supported.
>>
>> Suggested-by: Bjorn Helgaas <helgaas at kernel.org>
> I think this refers to the conversation at:
>
>    https://lore.kernel.org/r/20260113210259.GA715789@bhelgaas/
>
> Can you include that URL for reference?


Sure thing, I'll resend with a Link: (I guess that's the appropriate 
method) after a few days.

Thanks,

Caleb


>
>> Signed-off-by: Ahmed Naseef <naseefkm at gmail.com>
>> Signed-off-by: Caleb James DeLisle <cjd at cjdns.fr>
> Acked-by: Bjorn Helgaas <bhelgaas at google.com>
>
>> ---
>>   drivers/pci/probe.c | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
>> index bccc7a4bdd79..4eacb741b4ec 100644
>> --- a/drivers/pci/probe.c
>> +++ b/drivers/pci/probe.c
>> @@ -395,6 +395,9 @@ static void pci_read_bridge_io(struct pci_dev *dev, struct resource *res,
>>   	unsigned long io_mask, io_granularity, base, limit;
>>   	struct pci_bus_region region;
>>   
>> +	if (!dev->io_window)
>> +		return;
>> +
>>   	io_mask = PCI_IO_RANGE_MASK;
>>   	io_granularity = 0x1000;
>>   	if (dev->io_window_1k) {
>> @@ -465,6 +468,9 @@ static void pci_read_bridge_mmio_pref(struct pci_dev *dev, struct resource *res,
>>   	pci_bus_addr_t base, limit;
>>   	struct pci_bus_region region;
>>   
>> +	if (!dev->pref_window)
>> +		return;
>> +
>>   	pci_read_config_word(dev, PCI_PREF_MEMORY_BASE, &mem_base_lo);
>>   	pci_read_config_word(dev, PCI_PREF_MEMORY_LIMIT, &mem_limit_lo);
>>   	base64 = (mem_base_lo & PCI_PREF_RANGE_MASK) << 16;
>> -- 
>> 2.39.5
>>