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.

Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
---
Change from v3 to v4
- Add Bjorn's ack tag

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..4699b1208d621 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;
+	}
+
 	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

On Fri, 01 Nov 2024 21:04:39 +0000,
Frank Li <Frank.Li@nxp.com> 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.
> 
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
> Signed-off-by: Frank Li <Frank.Li@nxp.com>

I converted the fruity PCIe controller over to this infrastructure,
and things seem to work fine. FWIW:

Reviewed-by: Marc Zyngier <maz@kernel.org>
Tested-by: Marc Zyngier <maz@kernel.org>

	M.

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