Hi Ayan,
On 08/11/2024 20:00, Ayan Kumar Halder wrote:
CONFIG_EARLY_UART_SIZE is introduced to let user provide physical size of
early UART. Unlike MMU where we map a page in the virtual address space,
here we need to know the exact physical size to be mapped.
As VA == PA in case of MPU, the memory layout follows exactly the hardware
configuration. As a consequence, we set EARLY_UART_VIRTUAL_ADDRESS as physical
address.
Further, we check whether user-defined EARLY_UART_SIZE is aligned to PAGE_SIZE
(4KB). This is partly because we intend to map a minimum of 1 page(ie 4KB) and
the limit address is set as "EARLY_UART_SIZE-1". The limit address needs to end
with 0x3f (as required by PRLAR register).
Looking at the code below, it is not clear why you need to have
UART_SIZE 4KB-aligned. Furthermore...
UART is mapped as nGnRE region (as specified by ATTR=100 , refer G1.3.13,
MAIR_EL2, "---0100 Device memory nGnRE") and Doc ID - 102670_0101_02_en
Table 4-3, Armv8 architecture memory types (nGnRE - Corresponds to Device in
Armv7 architecture). Also, it is mapped as outer shareable, RW at EL2 only
and execution of instructions from the region is not permitted.
Signed-off-by: Ayan Kumar Halder <ayan.kumar.hal...@amd.com>
---
xen/arch/arm/Kconfig.debug | 7 +++++++
xen/arch/arm/arm64/mpu/head.S | 9 +++++++++
xen/arch/arm/include/asm/early_printk.h | 19 +++++++++++++++++++
3 files changed, 35 insertions(+)
diff --git a/xen/arch/arm/Kconfig.debug b/xen/arch/arm/Kconfig.debug
index 7660e599c0..84a0616102 100644
--- a/xen/arch/arm/Kconfig.debug
+++ b/xen/arch/arm/Kconfig.debug
@@ -121,6 +121,13 @@ config EARLY_UART_BASE_ADDRESS
hex "Early printk, physical base address of debug UART"
range 0x0 0xffffffff if ARM_32
+config EARLY_UART_SIZE
+ depends on EARLY_PRINTK
+ depends on MPU
+ hex "Early printk, physical size of debug UART"
+ range 0x0 0xffffffff if ARM_32
+ default 0x1000
+
config EARLY_UART_PL011_BAUD_RATE
depends on EARLY_UART_PL011
int "Early printk UART baud rate for pl011"
diff --git a/xen/arch/arm/arm64/mpu/head.S b/xen/arch/arm/arm64/mpu/head.S
index 731698aa3b..98422d7ed3 100644
--- a/xen/arch/arm/arm64/mpu/head.S
+++ b/xen/arch/arm/arm64/mpu/head.S
@@ -11,8 +11,10 @@
#define REGION_TEXT_PRBAR 0x38 /* SH=11 AP=10 XN=00 */
#define REGION_RO_PRBAR 0x3A /* SH=11 AP=10 XN=10 */
#define REGION_DATA_PRBAR 0x32 /* SH=11 AP=00 XN=10 */
+#define REGION_DEVICE_PRBAR 0x22 /* SH=10 AP=00 XN=10 */
#define REGION_NORMAL_PRLAR 0x0f /* NS=0 ATTR=111 EN=1 */
+#define REGION_DEVICE_PRLAR 0x09 /* NS=0 ATTR=100 EN=1 */
/*
* Macro to prepare and set a EL2 MPU memory region.
@@ -137,6 +139,13 @@ FUNC(enable_boot_cpu_mm)
ldr x2, =__bss_end
prepare_xen_region x0, x1, x2, x3, x4, x5
+#ifdef CONFIG_EARLY_PRINTK
+ /* Xen early UART section. */
+ ldr x1, =CONFIG_EARLY_UART_BASE_ADDRESS
+ ldr x2, =(CONFIG_EARLY_UART_BASE_ADDRESS + CONFIG_EARLY_UART_SIZE)
+ prepare_xen_region x0, x1, x2, x3, x4, x5, attr_prbar=REGION_DEVICE_PRBAR,
attr_prlar=REGION_DEVICE_PRLAR
... the documentation of prepare_xen_region suggests that the base UART
should be page-aligned. However, there are systems (although not sure
about MPU ones) where the base UART address is not page-aligned (this is
because multiple UARTs share the same page).
But I don't see any need to require page alignment here. I think the
alignment/size should be based on the minumum supported by the MPU. This
means the documentation in prepare_xen_region likely needs to be updated.
+#endif
+
b enable_mpu
ret
END(enable_boot_cpu_mm)
diff --git a/xen/arch/arm/include/asm/early_printk.h
b/xen/arch/arm/include/asm/early_printk.h
index 46a5e562dd..98fd52c4db 100644
--- a/xen/arch/arm/include/asm/early_printk.h
+++ b/xen/arch/arm/include/asm/early_printk.h
@@ -15,6 +15,24 @@
#ifdef CONFIG_EARLY_PRINTK
+#ifndef CONFIG_MMU
Shouldn't this be #ifdef CONFIG_MPU followed by...
+
+/*
+ * For MPU systems, there is no VMSA support in EL2, so we use VA == PA
+ * for EARLY_UART_VIRTUAL_ADDRESS.
+ */
+#define EARLY_UART_VIRTUAL_ADDRESS CONFIG_EARLY_UART_BASE_ADDRESS
+
+/*
+ * User-defined EARLY_UART_SIZE must be aligned to a PAGE_SIZE, or
+ * we may map more than necessary in MPU system.
+ */
+#if (EARLY_UART_SIZE % PAGE_SIZE) != 0
+#error "EARLY_UART_SIZE must be aligned to PAGE_SIZE"
+#endif
+
+#else
#elif CONFIG_MMU
+
/* need to add the uart address offset in page to the fixmap address */
#define EARLY_UART_VIRTUAL_ADDRESS \
(FIXMAP_ADDR(FIX_CONSOLE) + (CONFIG_EARLY_UART_BASE_ADDRESS & ~PAGE_MASK))
@@ -22,6 +40,7 @@
#define TEMPORARY_EARLY_UART_VIRTUAL_ADDRESS \
(TEMPORARY_FIXMAP_ADDR(FIX_CONSOLE) + (CONFIG_EARLY_UART_BASE_ADDRESS &
~PAGE_MASK))
+#endif /* CONFIG_MMU */
And finally
#else
# error ...
#endif
#endif /* !CONFIG_EARLY_PRINTK */
> > #endif
--
Julien Grall
