| Message ID | 1370397539-21653-1-git-send-email-dianders@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi, On Tue, Jun 04, 2013 at 06:58:59PM -0700, Doug Anderson wrote: > At boot, we've got a stack trace that looks something like this > (exynos5 as example) > * exynos5_map_io > * s3c_init_cpu > * exynos_init_io > * exynos5_dt_map_io > * paging_init > * setup_arch > > When paging_init() runs we'll lose any early MMU mappings that we > might have had to allow us access to S3C_VA_UART. We won't add those > mappings back in until after the SoC-specific map_io() function is > called. However, we print the CPU ID _right before_ we call the > SoC-specific function. Oops. > > > Things happen to work all right most of the time because the mapping > is sticking around in our TLB. ...but if we get really unlucky (like > me!) or we put an explicit flush_tlb_all() at the start of > exynos_init_io(), then things go boom. > > This patch moves the problematic printk() till after the cpu->map_io() > call. It also switches it over to pr_info(). This patch _doesn't_ > remove the questionable printks in the panic case, since we might get > lucky and the TLB might still let us print. This patch also adds a > few warnings to help others avoid similar headaches. This seems to be caused by not calling iotable_ini() in exynos_init_io() when a device tree is passed into the kernel, thus not setting up the mapping for the UART in that case. I think the solution is instead to map the uart earlier. The window of exposure is still there, but much smaller (and similar to how it always has been). In current upstream, if there is no map_io mach_desc entry at all, debug_ll_io_init() will be called on all platforms. Seems appropriate to call that explicitly before of_scan_flat_dt() in exynos_init_io() in this case. Or am I missing something? -Olof
Olof, On Tue, Jun 4, 2013 at 8:15 PM, Olof Johansson <olof@lixom.net> wrote: > This seems to be caused by not calling iotable_ini() in exynos_init_io() > when a device tree is passed into the kernel, thus not setting up the > mapping for the UART in that case. > > I think the solution is instead to map the uart earlier. The window of > exposure is still there, but much smaller (and similar to how it always > has been). > > In current upstream, if there is no map_io mach_desc entry at all, > debug_ll_io_init() will be called on all platforms. Seems appropriate > to call that explicitly before of_scan_flat_dt() in exynos_init_io() > in this case. Oh. Ummm, right. Yes, debug_ll_io_init() is exactly what's needed here instead of all the complexity of what I proposed. New patch coming shortly. Thanks! :) -Doug
diff --git a/arch/arm/mach-exynos/common.c b/arch/arm/mach-exynos/common.c index 027c9e7..8b51b0d 100644 --- a/arch/arm/mach-exynos/common.c +++ b/arch/arm/mach-exynos/common.c @@ -386,6 +386,13 @@ int __init exynos_fdt_map_chipid(unsigned long node, const char *uname, void __init exynos_init_io(struct map_desc *mach_desc, int size) { + /* + * WARNING: use of printk in this function or its children can be + * deadly. We've switched over to new page tables but haven't yet + * added S3C_VA_UART into the mapping. You might get lucky and see a + * printout work, but if you call flush_tlb_all() it will fail reliably. + */ + #ifdef CONFIG_OF if (initial_boot_params) of_scan_flat_dt(exynos_fdt_map_chipid, NULL); diff --git a/arch/arm/plat-samsung/init.c b/arch/arm/plat-samsung/init.c index 79d10fc..494cfbb 100644 --- a/arch/arm/plat-samsung/init.c +++ b/arch/arm/plat-samsung/init.c @@ -49,18 +49,20 @@ void __init s3c_init_cpu(unsigned long idcode, cpu = s3c_lookup_cpu(idcode, cputab, cputab_size); if (cpu == NULL) { + /* Questionable printk; S3C_VA_UART not mapped yet! */ printk(KERN_ERR "Unknown CPU type 0x%08lx\n", idcode); panic("Unknown S3C24XX CPU"); } - - printk("CPU %s (id 0x%08lx)\n", cpu->name, idcode); - if (cpu->map_io == NULL || cpu->init == NULL) { + /* Questionable printk; S3C_VA_UART not mapped yet! */ printk(KERN_ERR "CPU %s support not enabled\n", cpu->name); panic("Unsupported Samsung CPU"); } cpu->map_io(); + + /* IMPORTANT: call this after cpu->map_io() so we can print reliably */ + pr_info("CPU %s (id 0x%08lx)\n", cpu->name, idcode); } /* s3c24xx_init_clocks
At boot, we've got a stack trace that looks something like this (exynos5 as example) * exynos5_map_io * s3c_init_cpu * exynos_init_io * exynos5_dt_map_io * paging_init * setup_arch When paging_init() runs we'll lose any early MMU mappings that we might have had to allow us access to S3C_VA_UART. We won't add those mappings back in until after the SoC-specific map_io() function is called. However, we print the CPU ID _right before_ we call the SoC-specific function. Oops. Things happen to work all right most of the time because the mapping is sticking around in our TLB. ...but if we get really unlucky (like me!) or we put an explicit flush_tlb_all() at the start of exynos_init_io(), then things go boom. This patch moves the problematic printk() till after the cpu->map_io() call. It also switches it over to pr_info(). This patch _doesn't_ remove the questionable printks in the panic case, since we might get lucky and the TLB might still let us print. This patch also adds a few warnings to help others avoid similar headaches. Signed-off-by: Doug Anderson <dianders@chromium.org> --- arch/arm/mach-exynos/common.c | 7 +++++++ arch/arm/plat-samsung/init.c | 8 +++++--- 2 files changed, 12 insertions(+), 3 deletions(-)