Re: [flashrom] [PATCH RFC] Access PCI BARs through sysfs

[Stefan Tauner]

On Thu, 26 Feb 2015 13:53:13 -0800
Ed Swierk  wrote:
> On Thu, Feb 26, 2015 at 4:10 AM, Patrick Georgi  wrote:
> > 2015-02-26 1:57 GMT+01:00 Ed Swierk :
> > > Running flashrom on a Linux system with CONFIG_STRICT_DEVMEM=y, I can now
> > > successfully program the SPI flash on an Intel 10G NIC using the
> > > +#if !defined(__DJGPP__) && !defined(__LIBPAYLOAD__)
> > > +static void *pcidev_mapbar_sysfs(struct pci_dev *dev, const char *descr, int bar, off_t offset, size_t length)
> >
> > Isn't that actually Linux specific, instead of non-djgpp-or-libpayload specific?
>
> I suppose that's a safe assumption, though I don't know much about any
> of the other platforms flashrom supports. libpci already figures out
> whether the platform supports sysfs. I piggyback off that logic by
> checking pacc->method.
>
> Here we're just deciding whether the platform uses mmap() to access
> physical address space. I followed the same approach used in
> physmap.c, since pcidev_mapbar_sysfs() is doing the same thing as
> sys_physmap_rw_uncached(), just with a PCI resource file instead of
> /dev/mem.
>
> But I can switch to #if IS_LINUX if you think that's clearer. We can
> revisit that if and when some other sprouts a similar mmapped sysfs
> interface to PCI resources.

I have not really looked into the patch... but I did a little compile
test on top of r1885. I'll just let the buildbot speak for itself:
http://buildbot.flashrom.org/buildresults/flashrom-000164-Zcc/results.txt
sparc7 is expected to fail with r1885.

[PATCH RFC] Access PCI BARs through sysfs

[Ed Swierk]

Thanks for the feedback. I cleaned up the code so it should compile on
all the supported systems.

Only then did I discover a much simpler approach. It turns out that
Linux (recent versions, at least) allow selective mmap access to
/dev/mem even with various strict security features enabled. Simply
not calling iopl() solves the problem.

I've posted a new patch for review.

--Ed

On Sat, Feb 28, 2015 at 4:08 PM, Stefan Tauner
 wrote:
> On Thu, 26 Feb 2015 13:53:13 -0800
> Ed Swierk  wrote:
> > On Thu, Feb 26, 2015 at 4:10 AM, Patrick Georgi  wrote:
> > > 2015-02-26 1:57 GMT+01:00 Ed Swierk :
> > > > Running flashrom on a Linux system with CONFIG_STRICT_DEVMEM=y, I can now
> > > > successfully program the SPI flash on an Intel 10G NIC using the
> > > > +#if !defined(__DJGPP__) && !defined(__LIBPAYLOAD__)
> > > > +static void *pcidev_mapbar_sysfs(struct pci_dev *dev, const char *descr, int bar, off_t offset, size_t length)
> > >
> > > Isn't that actually Linux specific, instead of non-djgpp-or-libpayload specific?
> >
> > I suppose that's a safe assumption, though I don't know much about any
> > of the other platforms flashrom supports. libpci already figures out
> > whether the platform supports sysfs. I piggyback off that logic by
> > checking pacc->method.
> >
> > Here we're just deciding whether the platform uses mmap() to access
> > physical address space. I followed the same approach used in
> > physmap.c, since pcidev_mapbar_sysfs() is doing the same thing as
> > sys_physmap_rw_uncached(), just with a PCI resource file instead of
> > /dev/mem.
> >
> > But I can switch to #if IS_LINUX if you think that's clearer. We can
> > revisit that if and when some other sprouts a similar mmapped sysfs
> > interface to PCI resources.
>
> I have not really looked into the patch... but I did a little compile
> test on top of r1885. I'll just let the buildbot speak for itself:
> http://buildbot.flashrom.org/buildresults/flashrom-000164-Zcc/results.txt
> sparc7 is expected to fail with r1885.