Subject: Re: [PATCH v2 0/2] arm64: Cut rebuild time when changing CONFIG_BLK_DEV_INITRD

From: Mike Rapoport <[email-masked]>
Date: Thu, 25 Oct 2018 10:38:34 +0100

On Wed, Oct 24, 2018 at 02:55:17PM -0500, Rob Herring wrote:
> On Wed, Oct 24, 2018 at 2:33 PM Florian Fainelli <[email-masked]> wrote:
> >
> > Hi all,
> >
> > While investigating why ARM64 required a ton of objects to be rebuilt
> > when toggling CONFIG_DEV_BLK_INITRD, it became clear that this was
> > because we define __early_init_dt_declare_initrd() differently and we do
> > that in arch/arm64/include/asm/memory.h which gets included by a fair
> > amount of other header files, and translation units as well.
> 
> I scratch my head sometimes as to why some config options rebuild so
> much stuff. One down, ? to go. :)
> 
> > Changing the value of CONFIG_DEV_BLK_INITRD is a common thing with build
> > systems that generate two kernels: one with the initramfs and one
> > without. buildroot is one of these build systems, OpenWrt is also
> > another one that does this.
> >
> > This patch series proposes adding an empty initrd.h to satisfy the need
> > for drivers/of/fdt.c to unconditionally include that file, and moves the
> > custom __early_init_dt_declare_initrd() definition away from
> > asm/memory.h
> >
> > This cuts the number of objects rebuilds from 1920 down to 26, so a
> > factor 73 approximately.
> >
> > Apologies for the long CC list, please let me know how you would go
> > about merging that and if another approach would be preferable, e.g:
> > introducing a CONFIG_ARCH_INITRD_BELOW_START_OK Kconfig option or
> > something like that.
> 
> There may be a better way as of 4.20 because bootmem is now gone and
> only memblock is used. This should unify what each arch needs to do
> with initrd early. We need the physical address early for memblock
> reserving. Then later on we need the virtual address to access the
> initrd. Perhaps we should just change initrd_start and initrd_end to
> physical addresses (or add 2 new variables would be less invasive and
> allow for different translation than __va()). The sanity checks and
> memblock reserve could also perhaps be moved to a common location.
>
> Alternatively, given arm64 is the only oddball, I'd be fine with an
> "if (IS_ENABLED(CONFIG_ARM64))" condition in the default
> __early_init_dt_declare_initrd as long as we have a path to removing
> it like the above option.

I think arm64 does not have to redefine __early_init_dt_declare_initrd().
Something like this might be just all we need (completely untested,
probably it won't even compile):

diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 9d9582c..e9ca238 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -62,6 +62,9 @@ s64 memstart_addr __ro_after_init = -1;
 phys_addr_t arm64_dma_phys_limit __ro_after_init;
 
 #ifdef CONFIG_BLK_DEV_INITRD
+
+static phys_addr_t initrd_start_phys, initrd_end_phys;
+
 static int __init early_initrd(char *p)
 {
 	unsigned long start, size;
@@ -71,8 +74,8 @@ static int __init early_initrd(char *p)
 	if (*endp == ',') {
 		size = memparse(endp + 1, NULL);
 
-		initrd_start = start;
-		initrd_end = start + size;
+		initrd_start_phys = start;
+		initrd_end_phys = end;
 	}
 	return 0;
 }
@@ -407,14 +410,27 @@ void __init arm64_memblock_init(void)
 		memblock_add(__pa_symbol(_text), (u64)(_end - _text));
 	}
 
-	if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && initrd_start) {
+	if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) &&
+	    (initrd_start || initrd_start_phys)) {
+		/*
+		 * FIXME: ensure proper precendence between
+		 * early_initrd and DT when both are present
+		 */
+		if (initrd_start) {
+			initrd_start_phys = __phys_to_virt(initrd_start);
+			initrd_end_phys = __phys_to_virt(initrd_end);
+		} else if (initrd_start_phys) {
+			initrd_start = __va(initrd_start_phys);
+			initrd_end = __va(initrd_start_phys);
+		}
+
 		/*
 		 * Add back the memory we just removed if it results in the
 		 * initrd to become inaccessible via the linear mapping.
 		 * Otherwise, this is a no-op
 		 */
-		u64 base = initrd_start & PAGE_MASK;
-		u64 size = PAGE_ALIGN(initrd_end) - base;
+		u64 base = initrd_start_phys & PAGE_MASK;
+		u64 size = PAGE_ALIGN(initrd_end_phys) - base;
 
 		/*
 		 * We can only add back the initrd memory if we don't end up
@@ -458,7 +474,7 @@ void __init arm64_memblock_init(void)
 	 * pagetables with memblock.
 	 */
 	memblock_reserve(__pa_symbol(_text), _end - _text);
-#ifdef CONFIG_BLK_DEV_INITRD
+#if 0
 	if (initrd_start) {
 		memblock_reserve(initrd_start, initrd_end - initrd_start);

> Rob

-- 
Sincerely yours,
Mike.