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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Date:	Mon, 6 Jun 2016 14:59:47 +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>
Subject: Re: [PATCH] Introducing kernel option to force all PCI memory
 resources to be page aligned. Fixes issues with uio based drivers.

Hi Greg,

thanks for the response.
> > Some uio based PCI drivers (e.g. uio_cif) do not work if the assigned
> > PCI memory resources are not page aligned.
> > By using the kernel option "pci=resource_alignment" it is possible to
> > force single PCI boards to use page alignment for their memory resources.
> > However, this is fairly cumbersome if multiple of these cards are in use.
> > This patch adds another kernel option "pci=resources_page_aligned"
> > that allows to set the default alignment of PCI memory resources to be
> > page aligned.
> > Overwriting of this default alignment via "pci=resource_alignment" is
> > still possible.
> 
> This seems like a very large hammer for a very specific problem with a card
> that seems to be not-in-spec (I can't find anywhere that requires resources to
> be "page" aligned in the PCI spec).  Why not fix the firmware in these cards?
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...

Regards

Mathias