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

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Message-ID: <20241102111012.23zwz4et2qkafyca@thinkpad>
Date: Sat, 2 Nov 2024 16:40:12 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.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>,
	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 v3 1/2] PCI: Add enable_device() and disable_device()
 callbacks for bridges

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>
> ---
> Change from v2 to v3
> - use Bjorn suggest's commit message.
> - call disable_device() when error happen.
> 
> Change from v1 to v2
> - move enable(disable)device ops to pci_host_bridge
> ---
>  drivers/pci/pci.c   | 23 ++++++++++++++++++++++-
>  include/linux/pci.h |  2 ++
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 7d85c04fbba2a..5e0cb9b6f4d4f 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;
> @@ -2068,9 +2069,16 @@ 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 (err)
> +			return err;
> +	}

How about wrapping the enable/disable part in a helper?

	int pci_host_bridge_enable_device(dev);
	void pci_host_bridge_disable_device(dev);

The definition could be placed in drivers/pci/pci.h as an inline function.

- Mani

> +
>  	err = pcibios_enable_device(dev, bars);
>  	if (err < 0)
> -		return err;
> +		goto err_enable;
>  	pci_fixup_device(pci_fixup_enable, dev);
>  
>  	if (dev->msi_enabled || dev->msix_enabled)
> @@ -2085,6 +2093,13 @@ static int do_pci_enable_device(struct pci_dev *dev, int bars)
>  	}
>  
>  	return 0;
> +
> +err_enable:
> +	if (host_bridge && host_bridge->disable_device)
> +		 host_bridge->disable_device(host_bridge, dev);
> +
> +	return err;
> +
>  }
>  
>  /**
> @@ -2262,12 +2277,18 @@ 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 */
> 
> -- 
> 2.34.1
> 

-- 
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