Re: [PATCH v3 10/10] PCI: apple: Configure RID to SID mapper on device addition

[Marc Zyngier <maz@kernel.org>]

On Mon, 13 Sep 2021 21:45:13 +0100,
"Sven Peter" <sven@svenpeter.dev> wrote:
> 
> 
> 
> On Mon, Sep 13, 2021, at 20:25, Marc Zyngier wrote:
> > The Apple PCIe controller doesn't directly feed the endpoint's
> > Requester ID to the IOMMU (DART), but instead maps RIDs onto
> > Stream IDs (SIDs). The DART and the PCIe controller must thus
> > agree on the SIDs that are used for translation (by using
> > the 'iommu-map' property).
> > 
> > For this purpose, parse the 'iommu-map' property each time a
> > device gets added, and use the resulting translation to configure
> > the PCIe RID-to-SID mapper. Similarily, remove the translation
> > if/when the device gets removed.
> > 
> > This is all driven from a bus notifier which gets registered at
> > probe time. Hopefully this is the only PCI controller driver
> > in the whole system.
> > 
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > ---
> >  drivers/pci/controller/pcie-apple.c | 158 +++++++++++++++++++++++++++-
> >  1 file changed, 156 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/pcie-apple.c 
> > b/drivers/pci/controller/pcie-apple.c
> > index 76344223245d..68d71eabe708 100644
> > --- a/drivers/pci/controller/pcie-apple.c
> > +++ b/drivers/pci/controller/pcie-apple.c
> > @@ -23,8 +23,10 @@
> >  #include <linux/iopoll.h>
> >  #include <linux/irqchip/chained_irq.h>
> >  #include <linux/irqdomain.h>
> > +#include <linux/list.h>
> >  #include <linux/module.h>
> >  #include <linux/msi.h>
> > +#include <linux/notifier.h>
> >  #include <linux/of_irq.h>
> >  #include <linux/pci-ecam.h>
> >  
> > @@ -116,6 +118,8 @@
> >  #define   PORT_TUNSTAT_PERST_ACK_PEND	BIT(1)
> >  #define PORT_PREFMEM_ENABLE		0x00994
> >  
> > +#define MAX_RID2SID			64
> 
> Do these actually have 64 slots? I thought that was only for
> the Thunderbolt controllers and that these only had 16.

You are indeed right, and I blindly used the limit used in the
Correlium driver. Using entries from 16 onward result in a non booting
system. The registers do not fault though, and simply ignore writes. I
came up with an simple fix for this, see below.

> I never checked it myself though and it doesn't make much
> of a difference for now since only four different RIDs will
> ever be connected anyway.

Four? I guess the radios expose more than a single RID?

Thanks,

	M.

diff --git a/drivers/pci/controller/pcie-apple.c b/drivers/pci/controller/pcie-apple.c
index 68d71eabe708..ec9e7abd2aca 100644
--- a/drivers/pci/controller/pcie-apple.c
+++ b/drivers/pci/controller/pcie-apple.c
@@ -148,6 +148,7 @@ struct apple_pcie_port {
 	struct irq_domain	*domain;
 	struct list_head	entry;
 	DECLARE_BITMAP(		sid_map, MAX_RID2SID);
+	int			sid_map_sz;
 	int			idx;
 };
 
@@ -495,12 +496,12 @@ static int apple_pcie_setup_refclk(struct apple_pcie *pcie,
 	return 0;
 }
 
-static void apple_pcie_rid2sid_write(struct apple_pcie_port *port,
+static u32 apple_pcie_rid2sid_write(struct apple_pcie_port *port,
 				     int idx, u32 val)
 {
 	writel_relaxed(val, port->base + PORT_RID2SID(idx));
 	/* Read back to ensure completion of the write */
-	(void)readl_relaxed(port->base + PORT_RID2SID(idx));
+	return readl_relaxed(port->base + PORT_RID2SID(idx));
 }
 
 static int apple_pcie_setup_port(struct apple_pcie *pcie,
@@ -557,9 +558,16 @@ static int apple_pcie_setup_port(struct apple_pcie *pcie,
 	if (ret)
 		return ret;
 
-	/* Reset all RID/SID mappings */
-	for (i = 0; i < MAX_RID2SID; i++)
+	/* Reset all RID/SID mappings, and check for RAZ/WI registers */
+	for (i = 0; i < MAX_RID2SID; i++) {
+		if (apple_pcie_rid2sid_write(port, i, 0xbad1d) != 0xbad1d)
+			break;
 		apple_pcie_rid2sid_write(port, i, 0);
+	}
+
+	dev_dbg(pcie->dev, "%pOF: %d RID/SID mapping entries\n", np, i);
+
+	port->sid_map_sz = i;
 
 	list_add_tail(&port->entry, &pcie->ports);
 	init_completion(&pcie->event);
@@ -667,7 +675,7 @@ static int apple_pcie_add_device(struct pci_dev *pdev)
 		return err;
 
 	mutex_lock(&port->pcie->lock);
-	sid_idx = bitmap_find_free_region(port->sid_map, MAX_RID2SID, 0);
+	sid_idx = bitmap_find_free_region(port->sid_map, port->sid_map_sz, 0);
 	mutex_unlock(&port->pcie->lock);
 
 	if (sid_idx < 0)
@@ -696,7 +704,7 @@ static void apple_pcie_release_device(struct pci_dev *pdev)
 
 	mutex_lock(&port->pcie->lock);
 
-	for_each_set_bit(idx, port->sid_map, MAX_RID2SID) {
+	for_each_set_bit(idx, port->sid_map, port->sid_map_sz) {
 		u32 val;
 
 		val = readl_relaxed(port->base + PORT_RID2SID(idx));

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