Am Donnerstag, den 28.02.2019, 20:30 +0530 schrieb Vidya Sagar: > 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. So you are trading a slight memory waste of a single page against a sporadic (and probably hard to debug) DMA failure if any device happens to initiate DMA to the first page of physical memory? That does not sound like a good deal... Also why would the first page of external memory be unlikely to be used? Regards, Lucas > Original base patch was posted by Thierry Reding <treding@xxxxxxxxxx> > ( 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@xxxxxxxxxx> > --- > 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); >
