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Message-Id: <201510072201.51697.arnd@arndb.de> Date: Wed, 7 Oct 2015 22:01:49 +0200 From: Arnd Bergmann <arnd@...db.de> To: Krzysztof Hałasa <khalasa@...p.pl> Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] ARM: cns3xxx: pci: avoid potential stack overflow On Wednesday 27 May 2015, Krzysztof Hałasa wrote: > Arnd Bergmann <arnd@...db.de> writes: > > > The cns3xxx_pcie_hw_init function uses excessive kernel > > stack space because of a hack that puts a fake struct > > pci_sys_data and struct pci_bus on the stack in order to > > call the generic pci_bus_read_config accessors, which causes > > a warning in ARM allmodconfig builds: > > > > arch/arm/mach-cns3xxx/pcie.c:266:1: warning: the frame size of 1080 bytes is larger than 1024 bytes > > > > This rewrites the code in question to use a private > > implementation of the config space access for the same > > purpose, getting rid of the local variables and the > > warning in the process. As part of this, we have to > > use an open-coded version of pci_bus_find_capability(), > > which unfortunately complicates the implementation. > > Wouldn't it be better to simply use static structs for this purpose? > The hack isn't pretty, though. Hi Krzysztof, sorry for the late reply. I sent the patch shortly before my parental leave and have only now picked up this work again. I've looked at the driver once more and have come up with a modified approach that should hopefully address all the concerns. > > + regs = cnspci->cfg0_regs + (PCI_DEVFN(1, 0) << 12); > > + > > Some comment about would be helpful. Such as this: > > > > - bus.number = 1; /* directly connected PCIe device */ > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Agreed. I think I've managed to get rid of this part completely though. > > + pos = cns3xxx_pci_raw_read_config(regs, PCI_CAPABILITY_LIST, 1); > > + while (cns3xxx_pci_raw_read_config(regs, pos, 1) != PCI_CAP_ID_EXP) > > + pos = cns3xxx_pci_raw_read_config(regs, pos + PCI_CAP_LIST_NEXT, 1); > > + > > I wonder if this can fail (i.e., no PCI_CAP_ID_EXP capability). This is now gone too, so we no longer have to worry about it. I was mistakingly assuming that these were registers inside of the SoC rather than in the device that gets attached. > > + dc = cns3xxx_pci_raw_read_config(regs, pos + PCI_EXP_DEVCTL, 2); > > + dc &= ~(0x3 << 12); /* Clear Device Control Register [14:12] */ > > + cns3xxx_pci_raw_write_config(regs, pos + PCI_EXP_DEVCTL, 2, dc); > > + dc = cns3xxx_pci_raw_read_config(regs, pos + PCI_EXP_DEVCTL, 2); > > + if (!(dc & (0x3 << 12))) > > + pr_info("PCIe: Set Device Max_Read_Request_Size to 128 byte\n"); > > + > > This seems to revert 367dc4b75f4349d5363bc3ebdc030939db944786. Why do > you want to do it? My mistake. Gone too now. Thanks for your careful review back then! Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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