[U-Boot] [PATCH 3/3] PPC 85xx: Add qemu-ppce500 machine

[Scott Wood]

On Thu, 2014-01-23 at 14:08 +0100, Alexander Graf wrote:
> On 21.01.2014, at 03:25, Scott Wood <scottwood at freescale.com> wrote:
> 
> > On Sun, 2014-01-19 at 16:19 +0100, Alexander Graf wrote:
> >> For KVM we have a special PV machine type called "ppce500". This machine
> >> is inspired by the MPC8544DS board, but implements a lot less features
> >> than that one.
> >> 
> >> It also provides more PCI slots and is supposed to be enumerated by
> >> device tree only.
> >> 
> >> This patch adds support for the current generation ppce500 machine as
> >> it is implemented today.
> >> 
> >> Signed-off-by: Alexander Graf <agraf at suse.de>
> >> ---
> >> arch/powerpc/cpu/mpc85xx/start.S            |    7 +
> >> arch/powerpc/include/asm/config_mpc85xx.h   |    4 +
> >> board/freescale/qemu-ppce500/Makefile       |   10 ++
> >> board/freescale/qemu-ppce500/qemu-ppce500.c |  260 +++++++++++++++++++++++++++
> >> board/freescale/qemu-ppce500/tlb.c          |   59 ++++++
> >> boards.cfg                                  |    1 +
> >> include/configs/qemu-ppce500.h              |  235 ++++++++++++++++++++++++
> >> 7 files changed, 576 insertions(+)
> >> create mode 100644 board/freescale/qemu-ppce500/Makefile
> >> create mode 100644 board/freescale/qemu-ppce500/qemu-ppce500.c
> >> create mode 100644 board/freescale/qemu-ppce500/tlb.c
> >> create mode 100644 include/configs/qemu-ppce500.h
> >> 
> >> diff --git a/arch/powerpc/cpu/mpc85xx/start.S b/arch/powerpc/cpu/mpc85xx/start.S
> >> index db84d10..ccbcc03 100644
> >> --- a/arch/powerpc/cpu/mpc85xx/start.S
> >> +++ b/arch/powerpc/cpu/mpc85xx/start.S
> >> @@ -80,6 +80,13 @@ _start_e500:
> >> 	li	r1,MSR_DE
> >> 	mtmsr 	r1
> >> 
> >> +#ifdef CONFIG_QEMU_E500
> >> +	/* Save our ePAPR device tree off before we clobber it */
> >> +	lis	r2, CONFIG_QEMU_DT_ADDR at h
> >> +	ori	r2, r2, CONFIG_QEMU_DT_ADDR at l
> >> +	stw	r3, 0(r2)
> >> +#endif
> > 
> > r2 has a special purpose -- please don't use it for other things, even
> > if it's too early to be a problem and other code is similarly bad.
> 
> Heh, ok. I'll use r4 instead.
> 
> > Instead of saving the DT pointer in some random hardcoded address, how
> > about sticking it in a callee-saved register until you're able to store
> > it in the global data struct?
> 
> I did that at first but that didn't survive relocation. However, I just
> remembered that I had my global variable in bss, so maybe relocation
> doesn't work properly there. Instead I put it in .data now and that
> seems to work.
> 
> It's certainly the nicer solution, I agree.

I don't mean a global variable, but a field in the global data struct
(gd_t).  BSS should not be accessed, and global variables should not be
written, before relocation (although you may get away with the latter
pre-relocation in ramboot cases, you still shouldn't).

> >> +		/*
> >> +		 * We already know where the initrd is inside the dtb, so no
> >> +		 * need to override it
> >> +		 */
> >> +			setenv("ramdisk_addr", "-");
> > 
> > Indentation.
> > 
> > What if the user wants to specify the initrd from within U-Boot?  This
> > should be handled via the default environment, not by overriding the
> > user's choice.
> 
> I'm not sure I see the difference. We have the following default boot script:
> 
> #define CONFIG_BOOTCOMMAND             \
>        "test -n \"$kernel_addr\" && bootm $kernel_addr $ramdisk_addr $fdt_addr\0"
> 
> which is the only place where we actually use $ramdisk_addr. If a user
> wants to specify the initrd within U-Boot he can do that easily because
> he would specify his own boot command anyway, right?

Oh.  I was confusing it with the existing $ramdiskaddr.  So I'm changing
my objection to the fact that it's confusing. :-)

Likewise $fdt_addr versus $fdtaddr.

> Maybe I should rename kernel_addr to qemu_kernel_addr and drop
> ramdisk_addr completely in favor for a - in the bootm command? Yeah,
> I'll do that :).

OK.

> >> +	ret = fdt_open_into((void*)dt_base, fdt, dt_size);
> >> +	if (ret)
> >> +		panic("Couldn't open fdt");
> >> +
> >> +	memory = fdt_path_offset(fdt, "/memory");
> >> +	prop = fdt_getprop(fdt, memory, "reg", &len);
> >> +
> >> +	if (prop && len >= 16)
> >> +		return *(uint64_t*)(prop+8);
> >> +
> >> +	panic("Couldn't determine RAM size");
> >> +}
> > 
> > Again, there's no need to create a temporary fdt copy every time you
> > want to read from it.
> > 
> > What if memory doesn't start at zero (e.g. for e500v2 VFIO)?
> 
> In that case we're pretty broken regardless of determining the correct memory size. Can u-boot handle that case at all? How would this work?

U-Boot can handle this on other architectures.  Not sure about the PPC
code.
 
> >> +unsigned long
> >> +get_board_sys_clk(ulong dummy)
> >> +{
> >> +	/* The actual clock doesn't matter in a PV machine */
> >> +	return 33333333;
> >> +}
> > 
> > s/doesn't matter/doesn't exist/
> > 
> > Where is this used from?  Can it be skipped for this target?  Is the CPU
> > timebase handled properly?
> 
> Turns out it's not required at all. Must have been a dependency of something I threw away in between.

OK.  I'm still curious about how the timebase frequency is handled.
 
> >> +	/* Enter AS=1 */
> >> +	asm volatile(
> >> +		"mfmsr	%0			\n"
> >> +		"ori	%0, %0, 0x30		\n"
> >> +		"mtsrr1	%0			\n"
> >> +		"bl	1f			\n"
> >> +		"1:				\n"
> >> +		"mflr	%0			\n"
> >> +		"addi	%0, %0, 16		\n"
> >> +		"mtsrr0	%0			\n"
> >> +		"rfi				\n"
> >> +	: "=r"(tmp) : : "lr");
> >> +
> >> +	/* Now we live in AS=1, so we can flush all old maps */
> >> +	clear_ddr_tlbs(ram_size >> 20);
> >> +	/* and create new ones */
> >> +	setup_ddr_tlbs(ram_size >> 20);
> >> +
> >> +	/* Now we can safely go back to AS=0 */
> >> +	asm volatile(
> >> +		"mfmsr	%0			\n"
> >> +		"subi	%0, %0, 0x30		\n"
> >> +		"mtsrr1	%0			\n"
> >> +		"bl	1f			\n"
> >> +		"1:				\n"
> >> +		"mflr	%0			\n"
> >> +		"addi	%0, %0, 16		\n"
> >> +		"mtsrr0	%0			\n"
> >> +		"rfi				\n"
> >> +	: "=r"(tmp) : : "lr");
> >> +
> >> +	/* And remove our AS=1 map */
> >> +	disable_tlb(13);
> >> +}
> > 
> > Why aren't we already in AS1?  What code are you replacing with this?
> 
> I honestly don't know how it's supposed to work at all usually.

Usually we enter AS1 from start.S during early boot (see switch_as), and
return to AS0 later in start.S (see _start_cont) after calling
cpu_init_early_f().

> >> +#undef CONFIG_RESET_VECTOR_ADDRESS
> >> +#define CONFIG_RESET_VECTOR_ADDRESS	(0x1000000 - 4) /* 16 MB */
> > 
> > Does QEMU begin execution here, or at the ELF entry point?
> 
> At the ELF entry point. But I need to define this to something.

Set CONFIG_SYS_MPC85XX_NO_RESETVEC.
 
> >> +/* CONFIG_NUM_DDR_CONTROLLERS is defined in include/asm/config_mpc85xx.h */
> >> +#define CONFIG_DIMM_SLOTS_PER_CTLR	0
> >> +#define CONFIG_CHIP_SELECTS_PER_CTRL	0
> > 
> > Why are we including code that cares about this?
> 
> In file included from cpu.c:25:0:
> /root/u-boot/include/fsl_ddr_sdram.h:183:7: error: 'CONFIG_CHIP_SELECTS_PER_CTRL' undeclared here (not in a function)
> 
> So we don't include code, but we include a header that cares.

I see.  Would be nice to clean that up at some point, but OK for now.
 
> >> +/* Get RAM size from device tree */
> >> +#define CONFIG_DDR_SPD
> >> +
> >> +#define CONFIG_SYS_CLK_FREQ        33000000
> > 
> > Likewise.  BTW, this made up sysclock frequency doesn't match the one
> > you made up elsewhere.
> 
> speed.c: In function 'get_sys_info':
> speed.c:347:42: error: 'CONFIG_SYS_CLK_FREQ' undeclared (first use in this function)

What do we need from speed.c?

-Scott