From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Return-Path: Date: Tue, 3 May 2016 09:46:28 +0100 From: Lorenzo Pieralisi To: Jayachandran C Cc: Bjorn Helgaas , Tomasz Nowicki , Arnd Bergmann , Will Deacon , Catalin Marinas , rafael@kernel.org, Hanjun Guo , Sinan Kaya , jiang.liu@linux.intel.com, robert.richter@caviumnetworks.com, Marcin Wojtas , Liviu.Dudau@arm.com, David Daney , Wangyijing , Suravee.Suthikulpanit@amd.com, msalter@redhat.com, linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, linaro-acpi@lists.linaro.org, Jon Masters Subject: Re: [PATCH V6 09/13] pci, acpi: Support for ACPI based generic PCI host controller Message-ID: <20160503084628.GA31158@red-moon> References: <1460740008-19489-1-git-send-email-tn@semihalf.com> <1460740008-19489-10-git-send-email-tn@semihalf.com> <20160428214800.GG25125@localhost> <20160429083709.GA3249@red-moon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: List-ID: On Fri, Apr 29, 2016 at 11:05:34PM +0530, Jayachandran C wrote: > On Fri, Apr 29, 2016 at 2:07 PM, Lorenzo Pieralisi > wrote: > > On Thu, Apr 28, 2016 at 04:48:00PM -0500, Bjorn Helgaas wrote: > > > > [...] > > > >> > +static int pci_acpi_setup_ecam_mapping(struct acpi_pci_root *root, > >> > + struct acpi_pci_generic_root_info *ri) > >> > +{ > >> > + u16 seg = root->segment; > >> > + u8 bus_start = root->secondary.start; > >> > + u8 bus_end = root->secondary.end; > >> > + struct pci_config_window *cfg; > >> > + struct mcfg_entry *e; > >> > + phys_addr_t addr; > >> > + int err = 0; > >> > + > >> > + mutex_lock(&pci_mcfg_lock); > >> > >> What does this lock protect? The pci_mcfg_list should already be > >> initialized by the time we get there, and it should be immutable for > >> the life of the system. In fact, I would prefer if we could just > >> search the static table itself whenever we need it rather than caching > >> it in our own list. But I don't think we can easily do that because > >> acpi_table_parse() is __init. > >> > >> > + e = pci_mcfg_lookup(seg, bus_start); > >> > >> I would argue that we should check for _CBA first, and fall back to > >> MCFG if _CBA doesn't exist. > >> > >> > + if (!e) { > >> > + addr = acpi_pci_root_get_mcfg_addr(root->device->handle); > >> > >> IMO, acpi_pci_root_get_mcfg_addr() is misnamed. It should be > >> acpi_pci_config_base_addr() or similar. It definitely is not related > >> to MCFG. Not your fault, obviously. > >> > >> > + if (addr == 0) { > >> > + pr_err(PREFIX"%04x:%02x-%02x bus range error\n", > >> > + seg, bus_start, bus_end); > >> > + err = -ENOENT; > >> > + goto err_out; > >> > + } > >> > + } else { > >> > + if (bus_start != e->bus_start) { > >> > + pr_err("%04x:%02x-%02x bus range mismatch %02x\n", > >> > + seg, bus_start, bus_end, e->bus_start); > >> > + err = -EINVAL; > >> > + goto err_out; > >> > + } else if (bus_end != e->bus_end) { > >> > + pr_warn("%04x:%02x-%02x bus end mismatch %02x\n", > >> > + seg, bus_start, bus_end, e->bus_end); > >> > + bus_end = min(bus_end, e->bus_end); > >> > + } > >> > + addr = e->addr; > >> > + } > >> > >> I really don't think you need a lock around this, so you can factor > >> out the address lookup into something like: > >> > >> addr = acpi_pci_config_base_addr(...); > >> if (addr) > >> return addr; > >> > >> return acpi_pci_mcfg_lookup(seg, busn_res); > >> > >> You can check inside acpi_pci_mcfg_lookup() to make sure the entry you > >> find covers the entire [busn_res.start-busn_res.end] range and return > >> failure if it doesn't. At this point, I'm not sure it's worth it to > >> truncate the host bridge bus range to match something we find in MCFG. > >> > >> If the MCFG entry covers *more* than the host bridge range from _CRS, > >> that's fine. In any case, we have to be careful with the start address, > >> because the MCFG start address is always based on bus 0, but I think > >> pci_generic_ecam_create() expects the start address based on the > >> bus_start you pass to it. > > > > Yes, I spotted this too, it is unfortunate but DT and MCFG handle > > the ECAM regions differently. In DT the reg property is relative > > to bus_start - ie reg MMIO region maps config space starting at > > the first bus in bus-range: > > > > Documentation/devicetree/bindings/pci/host-generic-pci.txt > > > > in ACPI(MCFG) as you said it is always relative to bus 0, it is > > unfortunate but the address to be mapped should be computed > > differently in the ECAM layer. > > Can't this be handled by fixing up the address before passing to > pci_generic_ecam_create? Yes it can, you just need to apply the bus shift, given that we know it is ECAM anyway you can even add a macro in the ecam generic header to compute it, anyway that's a minor detail, we just should not forget to fix it. Lorenzo