Re: Why set .suppress_bind_attrs even though .remove() implemented?

From: Johan Hovold <johan@kernel.org>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: "Pali Rohár" <pali@kernel.org>,
	"Johan Hovold" <johan+linaro@kernel.org>,
	"Kishon Vijay Abraham I" <kishon@ti.com>,
	"Xiaowei Song" <songxiaowei@hisilicon.com>,
	"Binghui Wang" <wangbinghui@hisilicon.com>,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Ryder Lee" <ryder.lee@mediatek.com>,
	"Jianjun Wang" <jianjun.wang@mediatek.com>,
	linux-pci@vger.kernel.org, "Krzysztof Wilczyński" <kw@linux.com>,
	"Ley Foon Tan" <ley.foon.tan@intel.com>,
	linux-kernel@vger.kernel.org, "Marc Zyngier" <maz@kernel.org>
Subject: Re: Why set .suppress_bind_attrs even though .remove() implemented?
Date: Mon, 25 Jul 2022 15:25:49 +0200	[thread overview]
Message-ID: <Yt6Z3cBrVy1lVTp1@hovoldconsulting.com> (raw)
In-Reply-To: <20220722143858.GA1818206@bhelgaas>

[ +CC: maz ]

On Fri, Jul 22, 2022 at 09:38:58AM -0500, Bjorn Helgaas wrote:
> On Fri, Jul 22, 2022 at 03:26:44PM +0200, Johan Hovold wrote:
> > On Thu, Jul 21, 2022 at 05:21:22PM -0500, Bjorn Helgaas wrote:
> 
> > > qcom is a DWC driver, so all the IRQ stuff happens in
> > > dw_pcie_host_init().  qcom_pcie_remove() does call
> > > dw_pcie_host_deinit(), which calls irq_domain_remove(), but nobody
> > > calls irq_dispose_mapping().
> > > 
> > > I'm thoroughly confused by all this.  But I suspect that maybe I
> > > should drop the "make qcom modular" patch because it seems susceptible
> > > to this problem:
> > > 
> > >   https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/commit/?h=pci/ctrl/qcom&id=41b68c2d097e
> > 
> > That should not be necessary.
> > 
> > As you note above, interrupt handling is implemented in dwc core so if
> > there are any issue here at all, which I doubt, then all of the dwc
> > drivers that currently can be built as modules would all be broken and
> > this would need to be fixed in core.
> 
> I don't know yet whether there's an issue.  We need a clear argument
> for why there is or is not.  The fact that others might be broken is
> not an argument for breaking another one ;)

It's not breaking anything that is currently working, and if there's
some corner case during module unload, that's not the end of the world
either.

It's a feature useful for developers and no one expects remove code to
be perfect (e.g. resilient against someone trying to break it by doing
things in parallel, etc.).

> > I've been using the modular pcie-qcom patch for months now, unloading
> > and reloading the driver repeatedly to test power sequencing, without
> > noticing any problems whatsoever.
> 
> Pali's commit log suggests that unloading the module is not, by
> itself, enough to trigger the problem:
> 
>   https://lore.kernel.org/linux-pci/20220709161858.15031-1-pali@kernel.org/
> 
> Can you test the scenario he mentions?

Turns out the pcie-qcom driver does not support legacy interrupts so
there's no risk of there being any lingering mappings if I understand
things correctly.

Johan