linux-kernel - Re: [PATCH] lib/logic_pio: Fix overlap check for pio registery

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Message-ID: <006ad6ce-d6b2-59cb-8209-aca3f6e53fec@huawei.com>
Date:   Mon, 21 Dec 2020 11:24:55 +0800
From:   Jiahui Cen <cenjiahui@...wei.com>
To:     John Garry <john.garry@...wei.com>, <linux-kernel@...r.kernel.org>
CC:     Wei Xu <xuwei5@...ilicon.com>, Arnd Bergmann <arnd@...db.de>,
        "Bjorn Helgaas" <bhelgaas@...gle.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        <xieyingtai@...wei.com>
Subject: Re: [PATCH] lib/logic_pio: Fix overlap check for pio registery

Hi John,

On 2020/12/18 18:40, John Garry wrote:
> On 18/12/2020 06:23, Jiahui Cen wrote:
>> Since the [start, end) is a half-open interval, a range with the end equal
>> to the start of another range should not be considered as overlapped.
>>
>> Signed-off-by: Jiahui Cen <cenjiahui@...wei.com>
>> ---
>>   lib/logic_pio.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/lib/logic_pio.c b/lib/logic_pio.c
>> index f32fe481b492..445d611f1dc1 100644
>> --- a/lib/logic_pio.c
>> +++ b/lib/logic_pio.c
>> @@ -57,7 +57,7 @@ int logic_pio_register_range(struct logic_pio_hwaddr *new_range)
>>               new_range->flags == LOGIC_PIO_CPU_MMIO) {
>>               /* for MMIO ranges we need to check for overlap */
>>               if (start >= range->hw_start + range->size ||
>> -                end < range->hw_start) {
>> +                end <= range->hw_start) {
> 
> It looks like your change is correct, but should not really have an impact in practice since:
> a: BIOSes generally list ascending IO port CPU addresses
> b. there is space between IO port CPU address regions
> 
> Have you seen a problem here?
> 

No serious problem. I found it just when I was working on adding support of
pci expander bridge for Arm in QEMU. I found the IO window of some extended
root bus could not be registered when I inserted the extended buses' _CRS
info into DSDT table in the x86 way, which does not sort the buses.

Though root buses should be sorted in QEMU, would it be better to accept
those non-ascending IO windows?

BTW, for b, it seems to be no space between IO windows of different root buses
generated by EDK2. Or maybe I missed something obvious.

Thanks,
Jiahui