On 03.06.2016 13:38, Lorenzo Pieralisi wrote:
On Mon, May 30, 2016 at 05:14:20PM +0200, Tomasz Nowicki wrote:
In order to handle PCI config space regions properly in ACPI, new MCFG interface is defined which does sanity checks on MCFG table and keeps its root pointer. The user is able to lookup MCFG regions based on host bridge root structure and domain:bus_start:bus_end touple. Use pci_mmcfg_late_init old prototype to avoid another function name.
"According to PCI firmware specifications, on systems booting with ACPI, PCI configuration for a host bridge must be set-up through the MCFG table regions for non-hotpluggable bridges and _CBA method for hotpluggable ones.
Current MCFG table handling code, as implemented for x86, cannot be easily generalized owing to x86 specific quirks handling and related code, which makes it hard to reuse on other architectures.
In order to implement MCFG PCI configuration handling for new platforms booting with ACPI (eg ARM64) this patch re-implements MCFG handling from scratch in a streamlined fashion and provides (through a generic interface available to all arches):
- Simplified MCFG table parsing (executed through the pci_mmcfg_late_init() hook as in current x86)
- MCFG regions look-up interface through domain:bus_start:bus_end tuple
The new MCFG regions handling interface is added to generic ACPI code so that existing architectures (eg x86) can be moved over to it and architectures relying on MCFG for ACPI PCI config space can rely on it without having to resort to arch specific implementations."
[...]
+#include <linux/kernel.h> +#include <linux/pci.h> +#include <linux/pci-acpi.h>
+/* Root pointer to the mapped MCFG table */ +static struct acpi_table_mcfg *mcfg_table; +static int mcfg_entries;
+int pci_mcfg_lookup(struct acpi_pci_root *root) +{
- struct acpi_mcfg_allocation *mptr, *entry = NULL;
- struct resource *bus_res = &root->secondary;
- int i;
- if (mcfg_table) {
mptr = (struct acpi_mcfg_allocation *) &mcfg_table[1];for (i = 0; i < mcfg_entries && !entry; i++, mptr++)if (mptr->pci_segment == root->segment &&mptr->start_bus_number == bus_res->start)entry = mptr;- }
- /* not found, use _CBA if available, else error */
- if (!entry) {
if (root->mcfg_addr)return root->mcfg_addr;pr_err("%04x:%pR MCFG lookup failed\n", root->segment, bus_res);return -ENOENT;- } else if (root->mcfg_addr && entry->address != root->mcfg_addr) {
pr_warn("%04x:%pR CBA %pa != MCFG %lx, using CBA\n",root->segment, bus_res, &root->mcfg_addr,(unsigned long)entry->address);return 0;- }
- /* found matching entry, bus range check */
- if (entry->end_bus_number != bus_res->end) {
resource_size_t bus_end = min_t(resource_size_t,entry->end_bus_number, bus_res->end);pr_warn("%04x:%pR bus end mismatch, using %02lx\n",root->segment, bus_res, (unsigned long)bus_end);bus_res->end = bus_end;- }
- if (!root->mcfg_addr)
root->mcfg_addr = entry->address;Let's hope that no one will ever implement a hotplug bridge with config space starting at physical address 0x0.
Nit: You should define what the return value means. For success, once you return the _CBA address, once 0; this should be consistent.
As we decided to return CFG start address in root->mcfg_addr we should return 0 for the case (!entry) && (root->mcfg_addr). I'll fix it.
Anyway, this function is not easy to read but it may well be fine, I will let Bjorn decide what to do with corner cases:
a) _CBA is != 0 and you get a MCFG entry that matches its address (I am not sure that capping the _CRS bus numbers is PCI compliant in that case) b) bus_end capping, either you leave code as-is (that caps also _CRS) or just warn and fail if the bus->end numbers mismatch
Pending Bjorn's opinion on the above (and commit log update):
Reviewed-by: Lorenzo Pieralisi lorenzo.pieralisi@arm.com
Thanks, Tomasz