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From: Bjorn Helgaas <helgaas@kernel.org>
To: Oliver <oohall@gmail.com>
Cc: Shawn Anastasio <shawn@anastas.io>,
	linux-pci@vger.kernel.org,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Sam Bobroff <sbobroff@linux.ibm.com>,
	xyjxie@linux.vnet.ibm.com, rppt@linux.ibm.com,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 1/3] PCI: Introduce pcibios_ignore_alignment_request
Date: Wed, 29 May 2019 09:00:58 -0500	[thread overview]
Message-ID: <20190529140058.GB28250@google.com> (raw)
In-Reply-To: <CAOSf1CEFfbmwfvmdqT1xdt8SFb=tYdYXLfXeyZ8=iRnhg4a3Pg@mail.gmail.com>

On Tue, May 28, 2019 at 03:36:34PM +1000, Oliver wrote:
> On Tue, May 28, 2019 at 2:03 PM Shawn Anastasio <shawn@anastas.io> wrote:
> >
> > Introduce a new pcibios function pcibios_ignore_alignment_request
> > which allows the PCI core to defer to platform-specific code to
> > determine whether or not to ignore alignment requests for PCI resources.
> >
> > The existing behavior is to simply ignore alignment requests when
> > PCI_PROBE_ONLY is set. This is behavior is maintained by the
> > default implementation of pcibios_ignore_alignment_request.
> >
> > Signed-off-by: Shawn Anastasio <shawn@anastas.io>
> > ---
> >  drivers/pci/pci.c   | 9 +++++++--
> >  include/linux/pci.h | 1 +
> >  2 files changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 8abc843b1615..8207a09085d1 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -5882,6 +5882,11 @@ resource_size_t __weak pcibios_default_alignment(void)
> >         return 0;
> >  }
> >
> > +int __weak pcibios_ignore_alignment_request(void)
> > +{
> > +       return pci_has_flag(PCI_PROBE_ONLY);
> > +}
> > +
> >  #define RESOURCE_ALIGNMENT_PARAM_SIZE COMMAND_LINE_SIZE
> >  static char resource_alignment_param[RESOURCE_ALIGNMENT_PARAM_SIZE] = {0};
> >  static DEFINE_SPINLOCK(resource_alignment_lock);
> > @@ -5906,9 +5911,9 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
> >         p = resource_alignment_param;
> >         if (!*p && !align)
> >                 goto out;
> > -       if (pci_has_flag(PCI_PROBE_ONLY)) {
> > +       if (pcibios_ignore_alignment_request()) {
> >                 align = 0;
> > -               pr_info_once("PCI: Ignoring requested alignments (PCI_PROBE_ONLY)\n");
> > +               pr_info_once("PCI: Ignoring requested alignments\n");
> >                 goto out;
> >         }
> 
> I think the logic here is questionable to begin with. If the user has
> explicitly requested re-aligning a resource via the command line then
> we should probably do it even if PCI_PROBE_ONLY is set. When it breaks
> they get to keep the pieces.

I agree.  I don't like PCI_PROBE_ONLY in the first place.  It's a
sledgehammer approach that doesn't tell us which resource assignments
need to be preserved or why.  I'd rather use IORESOURCE_PCI_FIXED and
set it for the BARs where there's actually some sort of
hypervisor/firmware/OS dependency.

If there's a way to avoid another pciobios_*() weak function, that
would also be better.

Bjorn

  parent reply	other threads:[~2019-05-29 14:01 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-28  4:03 [PATCH v3 0/3] Allow custom PCI resource alignment on pseries Shawn Anastasio
2019-05-28  4:03 ` [PATCH v3 1/3] PCI: Introduce pcibios_ignore_alignment_request Shawn Anastasio
2019-05-28  5:36   ` Oliver
2019-05-28  5:50     ` Shawn Anastasio
2019-05-28  6:27     ` Alexey Kardashevskiy
2019-05-28  7:39       ` Shawn Anastasio
2019-05-30  3:39         ` Alexey Kardashevskiy
2019-05-30 22:49           ` Shawn Anastasio
2019-05-31  3:56             ` Alexey Kardashevskiy
2019-06-03  2:23               ` Shawn Anastasio
2019-06-03  5:02                 ` Alexey Kardashevskiy
2019-06-03  8:35                   ` Alexey Kardashevskiy
2019-06-03  9:12                     ` Shawn Anastasio
2019-05-29 14:00     ` Bjorn Helgaas [this message]
2019-05-30  6:55     ` [EXTERNAL] " Sam Bobroff
2019-05-30 22:33       ` Shawn Anastasio
2019-05-28  4:03 ` [PATCH v3 2/3] powerpc/64: Enable pcibios_after_init hook on ppc64 Shawn Anastasio
2019-05-28  4:03 ` [PATCH v3 3/3] powerpc/pseries: Allow user-specified PCI resource alignment after init Shawn Anastasio
2019-05-29 14:02   ` Bjorn Helgaas

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