MIPS: Add CDMM bus support

Add MIPS Common Device Memory Map (CDMM) support in the form of a bus in
the standard Linux device model. Each device attached via CDMM is
discoverable via an 8-bit type identifier and may contain a number of
blocks of memory mapped registers in the CDMM region. IRQs are expected
to be handled separately.

Due to the per-cpu (per-VPE for MT cores) nature of the CDMM devices,
all the driver callbacks take place from workqueues which are run on the
right CPU for the device in question, so that the driver doesn't need to
be as concerned about which CPU it is running on. Callbacks also exist
for when CPUs are taken offline, so that any per-CPU resources used by
the driver can be disabled so they don't get forcefully migrated. CDMM
devices are created as children of the CPU device they are attached to.

Any existing CDMM configuration by the bootloader will be inherited,
however platforms wishing to enable CDMM should implement the weak
mips_cdmm_phys_base() function (see asm/cdmm.h) so that the bus driver
knows where it should put the CDMM region in the physical address space
if the bootloader hasn't already enabled it.

A mips_cdmm_early_probe() function is also provided to allow early boot
or particularly low level code to set up the CDMM region and probe for a
specific device type, for example early console or KGDB IO drivers for
the EJTAG Fast Debug Channel (FDC) CDMM device.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/9599/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/bus/Kconfig b/drivers/bus/Kconfig
index b99729e36860..cbddbaddb347 100644
--- a/drivers/bus/Kconfig
+++ b/drivers/bus/Kconfig
@@ -20,6 +20,19 @@ config IMX_WEIM
 	  The WEIM(Wireless External Interface Module) works like a bus.
 	  You can attach many different devices on it, such as NOR, onenand.
 
+config MIPS_CDMM
+	bool "MIPS Common Device Memory Map (CDMM) Driver"
+	depends on CPU_MIPSR2
+	help
+	  Driver needed for the MIPS Common Device Memory Map bus in MIPS
+	  cores. This bus is for per-CPU tightly coupled devices such as the
+	  Fast Debug Channel (FDC).
+
+	  For this to work, either your bootloader needs to enable the CDMM
+	  region at an unused physical address on the boot CPU, or else your
+	  platform code needs to implement mips_cdmm_phys_base() (see
+	  asm/cdmm.h).
+
 config MVEBU_MBUS
 	bool
 	depends on PLAT_ORION