linux-kernel - Re: [PATCH] powerpc/powernv: Enable reset_devices parameter to issue a PHB reset

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Date:   Fri, 13 Oct 2017 19:37:27 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     "Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc:     gpiccoli@...ux.vnet.ibm.com, benh@...nel.crashing.org,
        paulus@...ba.org, maurosr@...ux.vnet.ibm.com
Subject: Re: [PATCH] powerpc/powernv: Enable reset_devices parameter to issue a PHB reset

"Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com> writes:

> During a kdump kernel boot in PowerPC, we request a reset of the
> PHBs to the FW. It makes sense, since if we are booting a kdump
> kernel it means we had some trouble before and we cannot rely in
> the adapters' health; they could be in a bad state, hence the
> reset is needed.
>
> But not only in a kdump kernel we could use this reset - there are
> situations, specially when debugging drivers, that we could break
> an adapter in a way it requires such reset. One can tell to just
> go ahead and reboot the machine, but happens that many times doing
> kexec is much faster, and so preferable than a full power cycle.
> Also, we could have situations in which adapters are in bad state
> due to adapter's FW issue, and only a PHB Fundamental Reset could
> revive them.
>
> This patch enables the reset_devices parameter to perform such reset.
> The parameter is barely used - only few drivers make use of it.
> This is a PowerPC-only change.
>
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@...ux.vnet.ibm.com>
> ---
> This patch was built/tested against powerpc/next branch.
>
> We recently had a situation in which i40e driver couldn't start,
> even after a full power cycle, due to a bug in its FW triggered
> by a DCB condition in switch (thanks Mauro for narrowing this).
> This patch enabled us to revive the adapter and use network
> while debugging.

I really dislike this.

You're basically saying the kernel can't work out how to get a device
working, so let's leave it up to the user.

The driver should be fixed to detect that the device is not responding
and request a reset.

cheers