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Support has been added to the OMAP IOMMU driver to fix a boot hang issue on OMAP remoteprocs with AMMU/Unicache, caused by an improper AMMU/Unicache state upon initial deassertion of the processor reset. The issue is described in detail in the next three paragraphs. All the Cortex M3/M4 IPU processor subsystems in OMAP SoCs have a AMMU/Unicache IP that dictates the memory attributes for addresses seen by the processor cores. The AMMU/Unicache is configured/enabled by the SCACHE_CONFIG.BYPASS bit - a value of 1 enables the cache and mandates all addresses accessed by M3/M4 be defined in the AMMU. This bit is not programmable from the host processor. The M3/M4 boot sequence starts out with the AMMU/Unicache in disabled state, and SYS/BIOS programs the AMMU regions and enables the Unicache during one of its initial boot steps. This SCACHE_CONFIG.BYPASS bit is however enabled by default whenever a RET reset is applied to the IP, irrespective of whether it was previously enabled or not. The AMMU registers lose their context whenever this reset is applied. The reset is effective as long as the MMU portion of the subsystem is enabled and clocked. This behavior is common to all the IPU and DSP subsystems that have an AMMU/Unicache. The IPU boot sequence involves enabling and programming the MMU, and loading the processor and releasing the reset(s) for the processor. The PM setup code currently sets the target state for most of the power domains to RET. The L2 MMU can be enabled, programmed and accessed properly just fine with the domain in hardware supervised mode, while the power domain goes through a RET->ON->RET transition during the programming sequence. However, the ON->RET transition asserts a RET reset, and the SCACHE_CONFIG.BYPASS bit gets auto-set. An AMMU fault is thrown immediately when the M3/M4 core's reset is released since the first instruction address itself will not be defined in any valid AMMU regions. The ON->RET transition happens automatically on the power domain after enabling the iommu due to the hardware supervised mode. This patch adds and invokes the .set_pwrdm_constraint pdata ops, if present, during the OMAP IOMMU enable and disable functions to resolve the above boot hang issue. The ops will allow to invoke a mach-omap2 layer API pwrdm_set_next_pwrst() in a multi-arch kernel environment. The ops also returns the current power domain state while enforcing the constraint so that the driver can store it and use it to set back the power domain state while releasing the constraint. The pdata ops implementation restricts the target power domain to ON during enable, and back to the original power domain state during disable, and thereby eliminating the conditions for the boot issue. The implementation is effective only when the original power domain state is either RET or OFF, and is a no-op when it is ON or INACTIVE. The .set_pwrdm_constraint ops need to be plugged in pdata-quirks for the affected remote processors to be able to boot properly. Note that the current issue is seen only on kernels with the affected power domains programmed to enter RET. For eg., IPU1 on DRA7xx is in a separate domain and is susceptible to this bug, while the IPU2 subsystem is within CORE power domain, and CORE RET is not supported on this SoC. IPUs on OMAP4 and OMAP5 are also susceptible since they are in CORE power domain, and CORE RET is a valid power target on these SoCs. Signed-off-by: Suman Anna <s-anna@ti.com> Signed-off-by: Joerg Roedel <jroedel@suse.de> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.