This patch was triggered by a remark from Russell that
introducing a call to the waituart (needed to fix debug prints
on the Qualcomm platforms) was dangerous because in some cases
this will involve waiting for a modem CTS (clear to send)
signal, and debug messages would maybe not work on platforms
with no modem connected to the UART port: they will just
hang waiting for the modem to assert CTS and this might never
happen.
Looking through all UART debug drivers implementing the waituart
macro I discovered that all users except two actually use this
macro to check if the UART is ready for TX, let's call this
TXRDY.
Only two debug UART drivers actually check for CTS:
- arch/arm/include/debug/8250.S
- arch/arm/include/debug/tegra.S
The former is very significant since the 8250 is possibly
the most common UART on the planet.
We have the following problem: the semantics of waituart are
ambiguous making it dangerous to introduce the macro to debug
code fixing debug prints for Qualcomm. To start to pry this
problem apart, this patch does the following:
- Convert all debug UART drivers to define two macros:
- waituartcts with the clear semantic to wait for CTS
to be asserted
- waituarttxrdy with the clear semantic to wait for the TX
capability of the UART to be ready
- When doing this take care to assign the right function to
each drivers macro, so they now do exactly the above.
- Update the three sites in the kernel invoking the waituart
macro to call waituartcts/waituarttxrdy in sequence, so that
the functional impact on the kernel should be zero.
After this we can start to change the code sites using this
code to do the right thing.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Enable low-level debugging support for RZ/A2M (r7s9210).
The RZA2MEVB board uses either SCIF2 (SDRAM enabled) or SCIF4 (HyperRAM
only) for the serial console.
Note that "SCIFA" serial ports on RZ/A2 SoCs use a compressed register
layout, hence add support for that to renesas-scif.S.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Add serial port debug macros for the SCIF(A) serial ports.
This includes all supported shmobile SoCs, except for EMEV2.
The configuration logic (both Kconfig and #ifdef) is more complicated than
one would expect, for several reasons:
1. Not all SoCs have the same serial devices, and they're not always
at the same addresses.
2. There are two different types: SCIF and SCIFA. Fortunately they can
easily be distinguished by physical address.
3. Not all boards use the same serial port for the console.
The defaults correspond to the boards that are supported in
mainline. If you want to use a different serial port, just change
the value of CONFIG_DEBUG_UART_PHYS, and the rest will auto-adapt.
4. debug_ll_io_init() maps the SCIF(A) registers to a fixed virtual
address. 0xfdxxxxxx was chosen, as it should lie below VMALLOC_END
= 0xff000000, and must not conflict with the 2 MiB reserved region
at PCI_IO_VIRT_BASE = 0xfee00000.
- On SoCs not using the legacy machine_desc.map_io(),
debug_ll_io_init() is called by the ARM core code.
- On SoCs using the legacy machine_desc.map_io(),
debug_ll_io_init() must be called explicitly. Calls are added
for r8a7740, r8a7779, sh7372, and sh73a0.
This was derived from the r8a7790 version by Laurent Pinchart.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
