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

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Message-ID: <20240928000752.GA99095@bhelgaas>
Date: Fri, 27 Sep 2024 19:07:52 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Frank Li <Frank.Li@....com>
Cc: 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, maz@...nel.org, p.zabel@...gutronix.de,
	robin.murphy@....com, will@...nel.org
Subject: Re: [PATCH 1/2] PCI: Add enable_device() and disable_device()
 callbacks for bridges

On Thu, Sep 26, 2024 at 06:07:47PM -0400, Frank Li wrote:
> Some PCIe bridges require special handling when enabling or disabling
> PCIe devices. For example, on the i.MX95 platform, a lookup table must be
> configured to inform the hardware how to convert pci_device_id to stream
> (bus master) ID, which is used by the IOMMU and MSI controller to identify
> bus master device.

I don't think you're talking about PCI-to-PCI bridges (including PCIe
Root Ports and Switch Ports).  Those are all standardized and don't do
anything with Requester IDs or Stream IDs.

A PCI host bridge, e.g., a PCIe Root Complex, might have to deal with
Stream IDs, and I think that's what you're enabling here.  If so, I
think the hooks should be in struct pci_host_bridge instead of
pci_ops.

> Enablement will be failure when there is not enough lookup table resource.
> Avoid DMA write to wrong position. That is the reason why pci_fixup_enable
> can't work since not return value for fixup function.
> 
> Signed-off-by: Frank Li <Frank.Li@....com>
> ---
>  drivers/pci/pci.c   | 19 +++++++++++++++++++
>  include/linux/pci.h |  2 ++
>  2 files changed, 21 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 7d85c04fbba2a..e0f83ed53d964 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2057,6 +2057,7 @@ static int do_pci_enable_device(struct pci_dev *dev, int bars)
>  {
>  	int err;
>  	struct pci_dev *bridge;
> +	struct pci_bus *bus;
>  	u16 cmd;
>  	u8 pin;
>  
> @@ -2068,6 +2069,15 @@ static int do_pci_enable_device(struct pci_dev *dev, int bars)
>  	if (bridge)
>  		pcie_aspm_powersave_config_link(bridge);
>  
> +	bus = dev->bus;
> +	while (bus) {
> +		if (bus->ops->enable_device)
> +			err = bus->ops->enable_device(bus, dev);
> +		if (err)
> +			return err;
> +		bus = bus->parent;
> +	}
> +
>  	err = pcibios_enable_device(dev, bars);
>  	if (err < 0)
>  		return err;
> @@ -2262,12 +2272,21 @@ void pci_disable_enabled_device(struct pci_dev *dev)
>   */
>  void pci_disable_device(struct pci_dev *dev)
>  {
> +	struct pci_bus *bus;
> +
>  	dev_WARN_ONCE(&dev->dev, atomic_read(&dev->enable_cnt) <= 0,
>  		      "disabling already-disabled device");
>  
>  	if (atomic_dec_return(&dev->enable_cnt) != 0)
>  		return;
>  
> +	bus = dev->bus;
> +	while (bus) {
> +		if (bus->ops->disable_device)
> +			bus->ops->disable_device(bus, dev);
> +		bus = bus->parent;
> +	}
> +
>  	do_pci_disable_device(dev);
>  
>  	dev->is_busmaster = 0;
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 573b4c4c2be61..42c25b8efd538 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -803,6 +803,8 @@ static inline int pcibios_err_to_errno(int err)
>  struct pci_ops {
>  	int (*add_bus)(struct pci_bus *bus);
>  	void (*remove_bus)(struct pci_bus *bus);
> +	int (*enable_device)(struct pci_bus *bus, struct pci_dev *dev);
> +	void (*disable_device)(struct pci_bus *bus, struct pci_dev *dev);
>  	void __iomem *(*map_bus)(struct pci_bus *bus, unsigned int devfn, int where);
>  	int (*read)(struct pci_bus *bus, unsigned int devfn, int where, int size, u32 *val);
>  	int (*write)(struct pci_bus *bus, unsigned int devfn, int where, int size, u32 val);
> 
> -- 
> 2.34.1
>