BCM2711, Raspberry Pi 4's arm64 system on chip, contains a PCIe bus that can't handle 64-bit accesses to its MMIO address space. The issue has already been discussed here[1], and it turns out BCM2711 isn't the only broken device in the wild. In most cases, the solution to this issue is to convert writeq/readq() to into their lo_hi/hi_lo variants and the eventual introduction of some amount of locking. But that's not good enough for every device. For example, on some arm's SMMU configurations atomic 64-bit accesses are mandatory. This series tries to introduce a mechanism for drivers to be able to ascertain whether or not they are allowed to perform 64-bit accesses. The big question is the amount of granularity needed to deal with this (think here of distro images): - Build-time: if a broken platform included in the image, disallow any 64-bit access. Drivers that need 64-bit accesses could simply bypass the check and hope for the best. Imposes a performance penalty on otherwise well behaving platforms, and features that depend on 64bit access might be disabled unnecessarily. It's simple to implement, yet not very generic/future proof. - Run-time: allow/disallow 64-bit accesses based on boot time checks (i.e. check which platform the kernel is running on). Gets rid of all the negative aspects imposed to well-behaving platforms. Well-behaving buses can't coexist with broken ones while using all features. - Per-device: each device has its MMIO access properties and can take decisions based on its local bus. That said, I'm not aware of a system that absolutely needs this ATM. This series implements the third option mainly as a proof of concept. It's my personal preference on how to deal with this. That said, my main aim ATM is to settle on a general approach. Regards, Nicolas [1] https://lore.kernel.org/linux-arm-kernel/c188698ca0de3ed6c56a0cf7880e1578aa753077.camel@xxxxxxx/ --- Nicolas Saenz Julienne (13): dt-bindings: Introduce 64bit-mmio-broken driver core: Introduce MMIO configuration of: device: Introduce of_mmio_configure() driver core: plafrom: Introduce platform_mmio_configure() pci: Introduce pci_mmio_configure() device core: Introduce dev_64bit_mmio_supported() arm64: Mark ARCH_MVEBU as needing broken 64bit MMIO support arm64: dts: marvell: armada-ap80x: Mark config-space bus as 64bit-mmio-broken iommu/arm-smmu: Make use of dev_64bit_mmio_supported() iommu/arm-smmu-impl: Get rid of Marvell's implementation details arm64: Mark ARCH_BCM2835 as needing broken 64bit MMIO support ARM: dts: bcm2711: Mark PCIe bus as 64bit-mmio-broken scsi: megaraid: Make use of dev_64bit_mmio_supported() .../devicetree/bindings/common-properties.txt | 15 +++++++++++ arch/Kconfig | 8 ++++++ arch/arm/boot/dts/bcm2711.dtsi | 1 + arch/arm64/Kconfig.platforms | 2 ++ arch/arm64/boot/dts/marvell/armada-ap80x.dtsi | 1 + drivers/base/dd.c | 6 +++++ drivers/base/platform.c | 9 +++++++ drivers/iommu/arm/arm-smmu/arm-smmu-impl.c | 21 --------------- drivers/iommu/arm/arm-smmu/arm-smmu.c | 9 +++++++ drivers/iommu/arm/arm-smmu/arm-smmu.h | 9 +++++-- drivers/of/device.c | 19 ++++++++++++++ drivers/pci/pci-driver.c | 26 +++++++++++++++++++ drivers/scsi/megaraid/megaraid_sas_fusion.c | 23 ++++++++-------- include/linux/device.h | 20 ++++++++++++++ include/linux/device/bus.h | 3 +++ include/linux/of_device.h | 8 ++++++ 16 files changed, 145 insertions(+), 35 deletions(-) -- 2.30.1
