[PATCH] PCI: tegra: Do not allocate MSI target memory

From: Vidya Sagar <vidyas@nvidia.com>
To: <bhelgaas@google.com>, <lorenzo.pieralisi@arm.com>,
	<treding@nvidia.com>, <swarren@nvidia.com>,
	<mperttunen@nvidia.com>, <jonathanh@nvidia.com>
Cc: <linux-tegra@vger.kernel.org>, <linux-pci@vger.kernel.org>,
	<kthota@nvidia.com>, <mmaddireddy@nvidia.com>,
	<vidyas@nvidia.com>
Subject: [PATCH] PCI: tegra: Do not allocate MSI target memory
Date: Thu, 28 Feb 2019 20:30:04 +0530	[thread overview]
Message-ID: <1551366004-32547-1-git-send-email-vidyas@nvidia.com> (raw)

The PCI host bridge found on Tegra SoCs doesn't require the MSI target
address to be backed by physical system memory. Writes are intercepted
within the controller and never make it to the memory pointed to.

Since no actual system memory is required, remove the allocation of a
single page and hardcode the MSI target address with a special address
on a per-SoC basis. Ideally this would be an address to an MMIO memory
region (such as where the controller's register are located). However,
those addresses don't work reliably across all Tegra generations. The
only set of addresses that work consistently are those that point to
external memory.

This is not ideal, since those addresses could technically be used for
DMA and hence be confusing. However, the first page of external memory
is unlikely to be used and special enough to avoid confusion.

Original base patch was posted by Thierry Reding <treding@nvidia.com>
( http://patchwork.ozlabs.org/patch/848569/ )
Current patch removes hardcoding of external RAM starting address instead
gets it using memblock_start_of_DRAM() API

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
 drivers/pci/controller/pci-tegra.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/controller/pci-tegra.c b/drivers/pci/controller/pci-tegra.c
index f4f53d092e00..b33de7c78425 100644
--- a/drivers/pci/controller/pci-tegra.c
+++ b/drivers/pci/controller/pci-tegra.c
@@ -23,6 +23,7 @@
 #include <linux/irqdomain.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
+#include <linux/memblock.h>
 #include <linux/module.h>
 #include <linux/msi.h>
 #include <linux/of_address.h>
@@ -231,9 +232,8 @@ struct tegra_msi {
 	struct msi_controller chip;
 	DECLARE_BITMAP(used, INT_PCI_MSI_NR);
 	struct irq_domain *domain;
-	unsigned long pages;
 	struct mutex lock;
-	u64 phys;
+	phys_addr_t phys;
 	int irq;
 };
 
@@ -1548,9 +1548,7 @@ static int tegra_pcie_msi_setup(struct tegra_pcie *pcie)
 		goto err;
 	}
 
-	/* setup AFI/FPCI range */
-	msi->pages = __get_free_pages(GFP_KERNEL, 0);
-	msi->phys = virt_to_phys((void *)msi->pages);
+	msi->phys = memblock_start_of_DRAM();
 	host->msi = &msi->chip;
 
 	return 0;
@@ -1592,8 +1590,6 @@ static void tegra_pcie_msi_teardown(struct tegra_pcie *pcie)
 	struct tegra_msi *msi = &pcie->msi;
 	unsigned int i, irq;
 
-	free_pages(msi->pages, 0);
-
 	if (msi->irq > 0)
 		free_irq(msi->irq, pcie);
 
-- 
2.7.4

