From: <Kelvin.Cao@microchip.com>
To: <helgaas@kernel.org>
Cc: <kurt.schwemmer@microsemi.com>, <bhelgaas@google.com>,
<linux-pci@vger.kernel.org>, <kelvincao@outlook.com>,
<logang@deltatee.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/5] PCI/switchtec: Error out MRPC execution when no GAS access
Date: Fri, 8 Oct 2021 00:06:18 +0000 [thread overview]
Message-ID: <37d0615c8a9a5e7c55527f4d478a0e707292c1ec.camel@microchip.com> (raw)
In-Reply-To: <20211007212317.GA1268429@bhelgaas>
On Thu, 2021-10-07 at 16:23 -0500, Bjorn Helgaas wrote:
> On Wed, Oct 06, 2021 at 09:27:49PM +0000, Kelvin.Cao@microchip.com
> wrote:
> > On Wed, 2021-10-06 at 15:20 -0500, Bjorn Helgaas wrote:
> > > On Wed, Oct 06, 2021 at 07:00:55PM +0000,
> > > Kelvin.Cao@microchip.com
> > > wrote:
> > > So wait, you mean you just intentionally ask the firmware to
> > > reset, knowing that the device will be unusable until the user
> > > reboots or does a manual rescan? And the way to improve this is
> > > for the driver to report an error to the user instead of hanging?
> > > I *guess* that might be some sort of improvement, but seems like
> > > a
> > > pretty small one.
> >
> > Yes, however, I believe it's something our users really like to
> > have... With this, they can do their user space
> > programming/scripting more easily in a synchronous fashion.
> >
> > > > - The firwmare crashes and doesn't respond, which normally is
> > > > the reason for users to issue a firmware reset command to try
> > > > to recover it via either the driver or a sideband interface.
> > > > The firmware may not be able to recover by a reset in some
> > > > extream situations like hardware errors, so that an error
> > > > return is probably all the users can get before another level
> > > > of recovery happens.
> > > >
> > > > So I'd think this patch is still making the driver better in
> > > > some way.
>
> OK. I still think the fact that all these different mechanisms can
> reset the device behind your back and make the switch and anything on
> the other side of it just stop working is ..., well, let's just say
> it's quite surprising to me.
Actually there're mechanisms like permission control to limit what
people can do in the firmware, so I guess it's not as bad as it sounds
like.
>
> Well, at least this isn't quite so much a mystery anymore and maybe
> we
> can improve the commit log. E.g., maybe something like this:
>
> A firmware hard reset may be initiated by various mechanisms
> including a UART interface, TWI sideband interface from BMC, MRPC
> command from userspace, etc. The switchtec management driver is
> unaware of these resets.
>
> The reset clears PCI state including the BARs and Memory Space
> Enable bits, so the device no longer responds to the MMIO accesses
> the driver uses to operate it.
>
> MMIO reads to the device will fail with a PCIe error. When the
> root
> complex handles that error, it typically fabricates ~0 data to
> complete the CPU read.
>
> Check for this sort of error by reading the device ID from MMIO
> space. This ID can never be ~0, so if we see that value, it
> probably means the PCIe Memory Read failed and we should return an
> error indication to the application using the switchtec driver.
It looks good to me, the commit log removes the ambiguity. Let me know
if you prefer a v2 patchset with the updated commit log and naming
issue fix.
Thank you Bjorn for your patience and time!
Kelvin
next prev parent reply other threads:[~2021-10-08 0:06 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-24 11:08 [PATCH 0/5] Switchtec Fixes and Improvements kelvin.cao
2021-09-24 11:08 ` [PATCH 1/5] PCI/switchtec: Error out MRPC execution when no GAS access kelvin.cao
2021-10-01 20:18 ` Bjorn Helgaas
2021-10-01 20:29 ` Logan Gunthorpe
2021-10-01 23:49 ` Kelvin.Cao
2021-10-02 15:11 ` Bjorn Helgaas
2021-10-04 20:51 ` Kelvin.Cao
2021-10-05 20:11 ` Bjorn Helgaas
2021-10-06 0:37 ` Kelvin.Cao
2021-10-06 2:33 ` Bjorn Helgaas
2021-10-06 5:49 ` Kelvin.Cao
2021-10-06 14:19 ` Bjorn Helgaas
2021-10-06 19:00 ` Kelvin.Cao
2021-10-06 20:20 ` Bjorn Helgaas
2021-10-06 21:27 ` Kelvin.Cao
2021-10-07 21:23 ` Bjorn Helgaas
2021-10-08 0:06 ` Kelvin.Cao [this message]
2021-10-08 11:03 ` Bjorn Helgaas
2021-10-01 22:58 ` Kelvin.Cao
2021-10-01 23:52 ` Logan Gunthorpe
2021-10-02 0:05 ` Kelvin.Cao
2021-09-24 11:08 ` [PATCH 2/5] PCI/switchtec: Fix a MRPC error status handling issue kelvin.cao
2021-09-24 11:08 ` [PATCH 3/5] PCI/switchtec: Update the way of getting management VEP instance ID kelvin.cao
2021-09-24 11:08 ` [PATCH 4/5] PCI/switchtec: Replace ENOTSUPP with EOPNOTSUPP kelvin.cao
2021-09-24 11:08 ` [PATCH 5/5] PCI/switchtec: Add check of event support kelvin.cao
2021-09-24 15:53 ` [PATCH 0/5] Switchtec Fixes and Improvements Logan Gunthorpe
2021-09-25 5:27 ` Kelvin.Cao
2021-09-27 16:39 ` Bjorn Helgaas
2021-09-27 18:25 ` Kelvin.Cao
2021-10-08 17:05 ` Bjorn Helgaas
2021-10-08 17:23 ` Logan Gunthorpe
2021-10-08 18:25 ` Bjorn Helgaas
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