plat: rpi4: Skip UART initialisation
So far we have seen two different clock setups for the Raspberry Pi 4
board, with the VPU clock divider being different. This was handled by
reading the divider register and adjusting the base clock rate
accordingly.
Recently a new GPU firmware version appeared that changed the clock rate
*again*, though this time at a higher level, so the VPU rate (and the
apparent PLLC parent clock) did not seem to change, judging by reading
the clock registers.
So rather than playing cat and mouse with the GPU firmware or going
further down the rabbit hole of exploring the whole clock tree, let's
just skip the baud rate programming altogether. This works because the
GPU firmware actually sets up and programs the debug UART already, so
we can just use it.
Pass 0 as the base clock rate to let the console driver skip the setup,
also remove the no longer needed clock code.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: Ica88a3f3c9c11059357c1e6dd8f7a4d9b1f98fd7
diff --git a/plat/rpi/rpi4/rpi4_bl31_setup.c b/plat/rpi/rpi4/rpi4_bl31_setup.c
index 53ab0c2..9e3b539 100644
--- a/plat/rpi/rpi4/rpi4_bl31_setup.c
+++ b/plat/rpi/rpi4/rpi4_bl31_setup.c
@@ -119,8 +119,6 @@
u_register_t arg2, u_register_t arg3)
{
- uint32_t div_reg;
-
/*
* LOCAL_CONTROL:
* Bit 9 clear: Increment by 1 (vs. 2).
@@ -136,16 +134,12 @@
/*
* Initialize the console to provide early debug support.
- * Different GPU firmware revisions set up the VPU divider differently,
- * so read the actual divider register to learn the UART base clock
- * rate. The divider is encoded as a 12.12 fixed point number, but we
- * just care about the integer part of it.
+ * We rely on the GPU firmware to have initialised the UART correctly,
+ * as the baud base clock rate differs across GPU firmware revisions.
+ * Providing a base clock of 0 lets the 16550 UART init routine skip
+ * the initial enablement and baud rate setup.
*/
- div_reg = mmio_read_32(RPI4_CLOCK_BASE + RPI4_VPU_CLOCK_DIVIDER);
- div_reg = (div_reg >> 12) & 0xfff;
- if (div_reg == 0)
- div_reg = 1;
- rpi3_console_init(PLAT_RPI4_VPU_CLK_RATE / div_reg);
+ rpi3_console_init(0);
bl33_image_ep_info.pc = plat_get_ns_image_entrypoint();
bl33_image_ep_info.spsr = rpi3_get_spsr_for_bl33_entry();