linux-kernel - Re: [PATCH V4 4/6] PCI: tegra: Continue unconfig sequence even if parts fail

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Message-ID: <X8ZSGCdp3lqORsPh@ulmo>
Date:   Tue, 1 Dec 2020 15:24:24 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     Vidya Sagar <vidyas@...dia.com>, robh+dt@...nel.org,
        bhelgaas@...gle.com, jonathanh@...dia.com,
        amanharitsh123@...il.com, dinghao.liu@....edu.cn, kw@...ux.com,
        linux-pci@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, kthota@...dia.com,
        mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V4 4/6] PCI: tegra: Continue unconfig sequence even if
 parts fail

On Mon, Nov 30, 2020 at 12:10:07PM +0000, Lorenzo Pieralisi wrote:
> On Mon, Nov 09, 2020 at 10:49:35PM +0530, Vidya Sagar wrote:
> > Currently the driver checks for error value of different APIs during the
> > uninitialization sequence. It just returns from there if there is any error
> > observed for one of those calls. Comparatively it is better to continue the
> > uninitialization sequence irrespective of whether some of them are
> > returning error. That way, it is more closer to complete uninitialization.
> 
> Hi Vidya, Thierry,
> 
> I can apply this series (dropping patches as suggested by Thierry),
> before though I wanted to ask you if this patch is really an
> improvement, it is hard to understand why skipping some error
> codes is OK for device correct operations to continue, maybe it
> is worth describing why some of those failures aren't really
> fatal.
> 
> Please let me know, thanks.

As explained in the commit message, the idea is to continue tearing
down even if things fail somewhere in the middle, because that ensures
that the hardware gets as close to an "uninitialized" state as possible.
If for example the first reset assert were to fail, then none of the
PHYs get disabled, the regulator stays on and the clocks stays on, all
of which can continue draining power after the controller has already
been torn down.

So yes, I think this is an improvement. It's unclear to me what you're
asking for, though. Would you rather have a comment somewhere near the
tegra_pcie_unconfig_controller() function that states the same thing as
the commit message?

Thierry

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