linux-kernel - Re: [PATCH] PCI: merge slot and bus reset implementations

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Message-ID: <YG21k6/4QQNrw41S@unreal>
Date:   Wed, 7 Apr 2021 16:37:23 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     "ameynarkhede03@...il.com" <ameynarkhede03@...il.com>
Cc:     Raphael Norwitz <raphael.norwitz@...anix.com>,
        AlexWilliamson@...hlinux, alex.williamson@...hat.com,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: merge slot and bus reset implementations

On Wed, Apr 07, 2021 at 06:36:01PM +0530, ameynarkhede03@...il.com wrote:
> On 21/04/07 03:30PM, Leon Romanovsky wrote:
> > On Wed, Apr 07, 2021 at 01:53:56PM +0530, ameynarkhede03@...il.com wrote:
> > > On 21/04/07 10:23AM, Leon Romanovsky wrote:
> > > > On Tue, Apr 06, 2021 at 08:16:26AM -0600, Alex Williamson wrote:
> > > > > On Sun, 4 Apr 2021 11:04:32 +0300
> > > > > Leon Romanovsky <leon@...nel.org> wrote:
> > > > >
> > > > > > On Thu, Apr 01, 2021 at 10:56:16AM -0600, Alex Williamson wrote:
> > > > > > > On Thu, 1 Apr 2021 15:27:37 +0300
> > > > > > > Leon Romanovsky <leon@...nel.org> wrote:
> > > > > > >
> > > > > > > > On Thu, Apr 01, 2021 at 05:37:16AM +0000, Raphael Norwitz wrote:
> > > > > > > > > Slot resets are bus resets with additional logic to prevent a device
> > > > > > > > > from being removed during the reset. Currently slot and bus resets have
> > > > > > > > > separate implementations in pci.c, complicating higher level logic. As
> > > > > > > > > discussed on the mailing list, they should be combined into a generic
> > > > > > > > > function which performs an SBR. This change adds a function,
> > > > > > > > > pci_reset_bus_function(), which first attempts a slot reset and then
> > > > > > > > > attempts a bus reset if -ENOTTY is returned, such that there is now a
> > > > > > > > > single device agnostic function to perform an SBR.
> > > > > > > > >
> > > > > > > > > This new function is also needed to add SBR reset quirks and therefore
> > > > > > > > > is exposed in pci.h.
> > > > > > > > >
> > > > > > > > > Link: https://lkml.org/lkml/2021/3/23/911
> > > > > > > > >
> > > > > > > > > Suggested-by: Alex Williamson <alex.williamson@...hat.com>
> > > > > > > > > Signed-off-by: Amey Narkhede <ameynarkhede03@...il.com>
> > > > > > > > > Signed-off-by: Raphael Norwitz <raphael.norwitz@...anix.com>
> > > > > > > > > ---
> > > > > > > > >  drivers/pci/pci.c   | 17 +++++++++--------
> > > > > > > > >  include/linux/pci.h |  1 +
> > > > > > > > >  2 files changed, 10 insertions(+), 8 deletions(-)
> > > > > > > > >
> > > > > > > > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > > > > > > > > index 16a17215f633..12a91af2ade4 100644
> > > > > > > > > --- a/drivers/pci/pci.c
> > > > > > > > > +++ b/drivers/pci/pci.c
> > > > > > > > > @@ -4982,6 +4982,13 @@ static int pci_dev_reset_slot_function(struct pci_dev *dev, int probe)
> > > > > > > > >  	return pci_reset_hotplug_slot(dev->slot->hotplug, probe);
> > > > > > > > >  }
> > > > > > > > >
> > > > > > > > > +int pci_reset_bus_function(struct pci_dev *dev, int probe)
> > > > > > > > > +{
> > > > > > > > > +	int rc = pci_dev_reset_slot_function(dev, probe);
> > > > > > > > > +
> > > > > > > > > +	return (rc == -ENOTTY) ? pci_parent_bus_reset(dev, probe) : rc;
> > > > > > > >
> > > > > > > > The previous coding style is preferable one in the Linux kernel.
> > > > > > > > int rc = pci_dev_reset_slot_function(dev, probe);
> > > > > > > > if (rc != -ENOTTY)
> > > > > > > >   return rc;
> > > > > > > > return pci_parent_bus_reset(dev, probe);
> > > > > > >
> > > > > > >
> > > > > > > That'd be news to me, do you have a reference?  I've never seen
> > > > > > > complaints for ternaries previously.  Thanks,
> > > > > >
> > > > > > The complaint is not to ternaries, but to the function call as one of
> > > > > > the parameters, that makes it harder to read.
> > > > >
> > > > > Sorry, I don't find a function call as a parameter to a ternary to be
> > > > > extraordinary, nor do I find it to be a discouraged usage model within
> > > > > the kernel.  This seems like a pretty low bar for hard to read code.
> > > >
> > > > It is up to us where this bar is set.
> > > >
> > > > Thanks
> > > On the side note there are plenty of places where this pattern is used
> > > though
> > > for example -
> > > kernel/time/clockevents.c:328:
> > > return force ? clockevents_program_min_delta(dev) : -ETIME;
> > >
> > > kernel/trace/trace_kprobe.c:233:
> > > return tk ? within_error_injection_list(trace_kprobe_address(tk)) :
> > >        false;
> > >
> > > kernel/signal.c:3104:
> > > return oset ? put_compat_sigset(oset, &old_set, sizeof(*oset)) : 0;
> > > etc
> >
> > Did you look when they were introduced?
> >
> > Thanks
> >
> that code trace_kprobe in 2 years old.
> If you want more recent example checkout
> drivers/pci/controller/pcie-brcmstb.c:1112,1117:
> return pcie->rescal ? brcm_phy_cntl(pcie, 1) : 0;
> which was introduced 7 months ago.
> There are lot of examples in pci.c also.

Yeah, I know, copy-paste is a powerful tool.

Can we please progress with this patch instead of doing
archaeological research?

Thanks

> 
> Thanks,
> Amey