linux-kernel - Re: Map PCI resource to user space problem.

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Message-ID: <BANLkTim9fBeY3L_+M9B5GECs8QtuAeUrTw@mail.gmail.com>
Date:	Mon, 20 Jun 2011 10:41:38 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Armin Schindler <armin@...ware.de>
Cc:	Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org
Subject: Re: Map PCI resource to user space problem.

+cc linux-pci

On Mon, Jun 20, 2011 at 10:38 AM, Armin Schindler <armin@...ware.de> wrote:
> On Mon, 20 Jun 2011, Armin Schindler wrote:
>>
>> Hello,
>>
>> when I try to map PCI resource of size < PAGE_SIZE to user space
>> with e.g. remap_pfn_range() the mapping seems to be created,
>> but the access to the PCI device just doesn't work (read returns 0xff).
>>
>> The same happens when using sysfs. The device has
>> # ls -al /sys/bus/pci/devices/0000\:02\:09.0/resource*
>> -rw------- 1 root root     512 Jun 20 11:33
>> /sys/bus/pci/devices/0000:02:09.0/resource0
>> -rw------- 1 root root     256 Jun 20 11:33
>> /sys/bus/pci/devices/0000:02:09.0/resource1
>> -rw------- 1 root root 8388608 Jun 20 11:33
>> /sys/bus/pci/devices/0000:02:09.0/resource2
>> -rw------- 1 root root  262144 Jun 20 11:33
>> /sys/bus/pci/devices/0000:02:09.0/resource3
>>
>> and when I mmap() resource0, a valid address is returned, but reading the
>> area always returns 0xff.
>>
>> Since a kernel driver can access resource0 here without problems when
>> using
>> ioremap(), I'm not sure what is wrong with the sysfs entry for user space
>> (or using remap_pfn_range() in own mmap function).
>> The only hint I have so far is the size, which is smaller than PAGE_SIZE.
>
> I found the reason. It is not the size of the resource.
> The resource0 is assigned to a not page-aligned address.
> Example, the pci resource0 has address 0xfe5ffc00. mmap()ing it will
> actually seems to map address 0xfe5ff000 and the user needs to add 0xc00 to
> the address returned by mmap().
>
> Armin
>
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