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Michal Orzel
4fa2272458
There are implementations of PL011 that can only handle 32-bit accesses
as oppose to the normal behavior where accesses are 8/16-bit wide. This
is usually advertised by setting a dt property 'reg-io-width' to 4.
Introduce CONFIG_EARLY_UART_PL011_MMIO32 Kconfig option to be able to
enable the use of 32-bit only accessors in PL011 early printk code.
Define macros PL011_{STRH,STRB,LDRH} to distinguish accessors for normal
case from 32-bit MMIO one and use them in arm32/arm64 pl011 early printk
code.
Update documentation accordingly.
Signed-off-by: Michal Orzel <michal.orzel@amd.com>
Tested-by: Henry Wang <Henry.Wang@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
43 lines
1.7 KiB
Plaintext
43 lines
1.7 KiB
Plaintext
How to enable early printk
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Early printk can only be enabled if CONFIG_DEBUG=y or in EXPERT mode. You
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may want to enable it if you are debugging code that executes before the
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console is initialized.
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Note that selecting this option will limit Xen to a single UART definition.
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Attempting to boot Xen image on a different platform *will not work*, so this
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option should not be enable for Xens that are intended to be portable.
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Select one of the "Early printk via * UART" in the choice possible for
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"Early printk" in the "Debugging options" of Kconfig. You will then need to
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set other options, which depends on the driver selected.
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CONFIG_EARLY_UART_BASE_ADDRESS is a mandatory argument, it is the base
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physical address of the UART to use.
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Other options depends on the driver selected:
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- 8250
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- CONFIG_EARLY_UART_8250_REG_SHIFT is, optionally, the left-shift to
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apply to the register offsets within the uart.
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- pl011
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- CONFIG_EARLY_UART_PL011_BAUD_RATE is, optionally, a baud rate which
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should be used to configure the UART at start of day.
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If CONFIG_EARLY_UART_PL011_BAUD_RATE is set to 0 then the code will
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not try to initialize the UART, so that bootloader or firmware
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settings can be used for maximum compatibility.
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- CONFIG_EARLY_UART_PL011_MMIO32 is, optionally, used to enable 32-bit
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only accesses to registers.
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- scif
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- CONFIG_EARLY_UART_SCIF_VERSION_* is, optionally, the interface version
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of the UART. Default to version NONE.
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- For all other uarts there are no additional options.
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As a convenience it is also possible to select from a list of
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predefined configurations available in the list of choice for "Early
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printk" for specific platform.
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By default early printk is disabled.
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