linux-kernel - Re: [PATCH v2 1/2] PCI: Add enable_device() and disable

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Message-ID: <a96794e0-76f6-4091-b4d4-d88d084ed2c2@arm.com>
Date: Thu, 3 Oct 2024 11:30:58 +0100
From: Robin Murphy <robin.murphy@....com>
To: 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>
Cc: 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, will@...nel.org
Subject: Re: [PATCH v2 1/2] PCI: Add enable_device() and disable_device()
 callbacks for bridges

On 2024-09-30 8:42 pm, 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.
> 
> 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>
> ---
> Change from v1 to v2
> - move enable(disable)device ops to pci_host_bridge
> ---
>   drivers/pci/pci.c   | 14 ++++++++++++++
>   include/linux/pci.h |  2 ++
>   2 files changed, 16 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 7d85c04fbba2a..fcdeb12622568 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2056,6 +2056,7 @@ int __weak pcibios_enable_device(struct pci_dev *dev, int bars)
>   static int do_pci_enable_device(struct pci_dev *dev, int bars)
>   {
>   	int err;
> +	struct pci_host_bridge *host_bridge;
>   	struct pci_dev *bridge;
>   	u16 cmd;
>   	u8 pin;
> @@ -2068,6 +2069,13 @@ static int do_pci_enable_device(struct pci_dev *dev, int bars)
>   	if (bridge)
>   		pcie_aspm_powersave_config_link(bridge);
>   
> +	host_bridge = pci_find_host_bridge(dev->bus);
> +	if (host_bridge && host_bridge->enable_device) {
> +		err = host_bridge->enable_device(host_bridge, dev);

If the intent is that this call may allocate host bridge resources, what 
about the existing error returns below? Should those now have a cleanup 
path to avoid a potential resource leak from here?

Thanks,
Robin.

> +		if (err)
> +			return err;
> +	}
> +
>   	err = pcibios_enable_device(dev, bars);
>   	if (err < 0)
>   		return err;
> @@ -2262,12 +2270,18 @@ void pci_disable_enabled_device(struct pci_dev *dev)
>    */
>   void pci_disable_device(struct pci_dev *dev)
>   {
> +	struct pci_host_bridge *host_bridge;
> +
>   	dev_WARN_ONCE(&dev->dev, atomic_read(&dev->enable_cnt) <= 0,
>   		      "disabling already-disabled device");
>   
>   	if (atomic_dec_return(&dev->enable_cnt) != 0)
>   		return;
>   
> +	host_bridge = pci_find_host_bridge(dev->bus);
> +	if (host_bridge && host_bridge->disable_device)
> +		host_bridge->disable_device(host_bridge, dev);
> +
>   	do_pci_disable_device(dev);
>   
>   	dev->is_busmaster = 0;
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 573b4c4c2be61..ac15b02e14ddd 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -578,6 +578,8 @@ struct pci_host_bridge {
>   	u8 (*swizzle_irq)(struct pci_dev *, u8 *); /* Platform IRQ swizzler */
>   	int (*map_irq)(const struct pci_dev *, u8, u8);
>   	void (*release_fn)(struct pci_host_bridge *);
> +	int (*enable_device)(struct pci_host_bridge *bridge, struct pci_dev *dev);
> +	void (*disable_device)(struct pci_host_bridge *bridge, struct pci_dev *dev);
>   	void		*release_data;
>   	unsigned int	ignore_reset_delay:1;	/* For entire hierarchy */
>   	unsigned int	no_ext_tags:1;		/* No Extended Tags */
>