linux-kernel - Re: [PATCH] Introducing kernel option to force all PCI memory resources to be page aligned. Fixes issues with uio based drivers.

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Message-ID: <ef1a9c8e1ef0439a84ad43c1a8f92d79@FE-MBX1012.de.bosch.com>
Date:	Wed, 8 Jun 2016 08:32:52 +0000
From:	"Koehrer Mathias (ETAS/ESW5)" <mathias.koehrer@...s.com>
To:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"hjk@...sjkoch.de" <hjk@...sjkoch.de>,
	"helgaas@...nel.org" <helgaas@...nel.org>
Subject: Re: [PATCH] Introducing kernel option to force all PCI memory
 resources to be page aligned. Fixes issues with uio based drivers.

Hi Greg,
> > > > The issue is not the firmware. The issue is that the Linux uio
> > > > driver
> > > > (here: uio_cif) does not work as uio_mmap() -> uio_mmap_physical()
> > > > does not do a mmap on physical memory that is not page aligned...
> > >
> > > Then why not fix the uio_cif driver?
> > The fix might be in uio and not in uio_cif. However
> > uio_mmap_physical() in uio.c has introduced checks to reject non page-
> aligned addresses.
> 
> Yes, because we had real problems with that in the past.
> 
> > These checks have been introduced somewhere in between kernel V3.2 and
> kernel V3.18.
> > Removing these checks again does not sound to me like a good idea...
> 
> I agree, you should fix your hardware :)
> 
> > The overall question is now if the UIO system is working at all with
> > non page aligned PCI memory resources. For me it looks as if this is not the
> case.
> 
> How is your system ending up with such alignment in the first place?
> What is the resource list after booting?
Here is the resource list of the relevant PCI board. The first memory resource has a size of 128k and is not page aligned.

0f:05.0 Bridge: PLX Technology, Inc. PCI9030 32-bit 33MHz PCI <-> IOBus Bridge (rev 01)
	Subsystem: PLX Technology, Inc. Hilscher CIF50-PB/DPS Profibus
	Flags: medium devsel, IRQ 23
	Memory at eae4f400 (32-bit, non-prefetchable) [size=128]
	I/O ports at 9800 [size=128]
	Memory at eae4c000 (32-bit, non-prefetchable) [size=8K]
	Capabilities: [40] Power Management version 1
	Capabilities: [48] CompactPCI hot-swap <?>
	Capabilities: [4c] Vital Product Data
	Kernel driver in use: hilscher

Regards

Mathias