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When a PL310 cache is used on a system that provides hardware coherency, the outer cache sync operation is useless, and can be skipped. Moreover, on some systems, it is harmful as it causes deadlocks between the Marvell coherency mechanism, the Marvell PCIe controller and the Cortex-A9. To avoid this, this commit introduces a new Device Tree property 'arm,io-coherent' for the L2 cache controller node, valid only for the PL310 cache. It identifies the usage of the PL310 cache in an I/O coherent configuration. Internally, it makes the driver disable the outer cache sync operation. Note that technically speaking, a fully coherent system wouldn't require any of the other .outer_cache operations. However, in practice, when booting secondary CPUs, these are not yet coherent, and therefore a set of cache maintenance operations are necessary at this point. This explains why we keep the other .outer_cache operations and only ->sync is disabled. While in theory any write to a PL310 register could cause the deadlock, in practice, disabling ->sync is sufficient to workaround the deadlock, since the other cache maintenance operations are only used in very specific situations. Contrary to previous versions of this patch, this new version does not simply NULL-ify the ->sync member, because the l2c_init_data structures are now 'const' and therefore cannot be modified, which is a good thing. Therefore, this patch introduces a separate l2c_init_data instance, called of_l2c310_coherent_data. Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
63 lines
2.7 KiB
Plaintext
63 lines
2.7 KiB
Plaintext
* ARM L2 Cache Controller
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ARM cores often have a separate level 2 cache controller. There are various
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implementations of the L2 cache controller with compatible programming models.
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The ARM L2 cache representation in the device tree should be done as follows:
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Required properties:
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- compatible : should be one of:
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"arm,pl310-cache"
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"arm,l220-cache"
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"arm,l210-cache"
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"bcm,bcm11351-a2-pl310-cache": DEPRECATED by "brcm,bcm11351-a2-pl310-cache"
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"brcm,bcm11351-a2-pl310-cache": For Broadcom bcm11351 chipset where an
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offset needs to be added to the address before passing down to the L2
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cache controller
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"marvell,aurora-system-cache": Marvell Controller designed to be
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compatible with the ARM one, with system cache mode (meaning
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maintenance operations on L1 are broadcasted to the L2 and L2
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performs the same operation).
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"marvell,aurora-outer-cache": Marvell Controller designed to be
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compatible with the ARM one with outer cache mode.
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"marvell,tauros3-cache": Marvell Tauros3 cache controller, compatible
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with arm,pl310-cache controller.
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- cache-unified : Specifies the cache is a unified cache.
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- cache-level : Should be set to 2 for a level 2 cache.
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- reg : Physical base address and size of cache controller's memory mapped
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registers.
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Optional properties:
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- arm,data-latency : Cycles of latency for Data RAM accesses. Specifies 3 cells of
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read, write and setup latencies. Minimum valid values are 1. Controllers
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without setup latency control should use a value of 0.
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- arm,tag-latency : Cycles of latency for Tag RAM accesses. Specifies 3 cells of
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read, write and setup latencies. Controllers without setup latency control
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should use 0. Controllers without separate read and write Tag RAM latency
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values should only use the first cell.
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- arm,dirty-latency : Cycles of latency for Dirty RAMs. This is a single cell.
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- arm,filter-ranges : <start length> Starting address and length of window to
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filter. Addresses in the filter window are directed to the M1 port. Other
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addresses will go to the M0 port.
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- arm,io-coherent : indicates that the system is operating in an hardware
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I/O coherent mode. Valid only when the arm,pl310-cache compatible
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string is used.
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- interrupts : 1 combined interrupt.
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- cache-id-part: cache id part number to be used if it is not present
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on hardware
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- wt-override: If present then L2 is forced to Write through mode
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Example:
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L2: cache-controller {
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compatible = "arm,pl310-cache";
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reg = <0xfff12000 0x1000>;
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arm,data-latency = <1 1 1>;
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arm,tag-latency = <2 2 2>;
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arm,filter-ranges = <0x80000000 0x8000000>;
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cache-unified;
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cache-level = <2>;
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interrupts = <45>;
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};
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