linux-kernel - Re: [PATCH v3 1/2] PCI: Add enable_device() and disable

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Message-ID: <86ldy228nh.wl-maz@kernel.org>
Date: Fri, 01 Nov 2024 16:58:26 +0000
From: Marc Zyngier <maz@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Frank Li <Frank.Li@....com>,	Bjorn Helgaas <bhelgaas@...gle.com>,
	Richard Zhu <hongxing.zhu@....com>,	Lucas Stach <l.stach@...gutronix.de>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,	Krzysztof Wilczyński <kw@...ux.com>,	Manivannan Sadhasivam
 <manivannan.sadhasivam@...aro.org>,	Rob Herring <robh@...nel.org>,	Shawn
 Guo <shawnguo@...nel.org>,	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,	Fabio Estevam
 <festevam@...il.com>,	linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org,	linux-arm-kernel@...ts.infradead.org,
	imx@...ts.linux.dev,	alyssa@...enzweig.io,	bpf@...r.kernel.org,
	broonie@...nel.org,	jgg@...pe.ca,	joro@...tes.org,	lgirdwood@...il.com,
	p.zabel@...gutronix.de,	robin.murphy@....com,	will@...nel.org
Subject: Re: [PATCH v3 1/2] PCI: Add enable_device() and disable_device() callbacks for bridges

On Wed, 30 Oct 2024 21:00:43 +0000,
Bjorn Helgaas <helgaas@...nel.org> wrote:
> 
> On Thu, Oct 24, 2024 at 06:34:44PM -0400, Frank Li wrote:
> > Some PCIe host bridges require special handling when enabling or disabling
> > PCIe Endpoints. For example, the i.MX95 platform has a lookup table to map
> > Requester IDs to StreamIDs, which are used by the SMMU and MSI controller
> > to identify the source of DMA accesses.
> > 
> > Without this mapping, DMA accesses may target unintended memory, which
> > would corrupt memory or read the wrong data.
> > 
> > Add a host bridge .enable_device() hook the imx6 driver can use to
> > configure the Requester ID to StreamID mapping. The hardware table isn't
> > big enough to map all possible Requester IDs, so this hook may fail if no
> > table space is available. In that case, return failure from
> > pci_enable_device().
> > 
> > It might make more sense to make pci_set_master() decline to enable bus
> > mastering and return failure, but it currently doesn't have a way to return
> > failure.
> > 
> > Signed-off-by: Frank Li <Frank.Li@....com>
> 
> Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
> 
> Merge along with the imx6 change.

It'd be good to have this on a stable branch somewhere so that I can
refer to it when posting the conversion for the Apple driver to that
infrastructure, removing the need for a bus notifier.

Otherwise, I'll just cherry-pick that patch and post the whole thing.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.