linux-kernel - [PATCH] powerpc/40x: Map 32Mbytes of memory at startup

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Message-Id: <e2b142ad4a44535d5aa81b0c00c5f05f312f9097.1632738876.git.christophe.leroy@csgroup.eu>
Date:   Mon, 27 Sep 2021 12:34:52 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        cp <carlojpisani@...il.com>
Subject: [PATCH] powerpc/40x: Map 32Mbytes of memory at startup

As reported by Carlo, 16Mbytes is not enough with modern kernels
that tend to be a bit big, so map another 16M page at boot.

Cc: cp <carlojpisani@...il.com>
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 arch/powerpc/kernel/head_40x.S | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/head_40x.S b/arch/powerpc/kernel/head_40x.S
index 7d72ee5ab387..5fce4680d2d3 100644
--- a/arch/powerpc/kernel/head_40x.S
+++ b/arch/powerpc/kernel/head_40x.S
@@ -650,7 +650,7 @@ start_here:
 	b	.		/* prevent prefetch past rfi */
 
 /* Set up the initial MMU state so we can do the first level of
- * kernel initialization.  This maps the first 16 MBytes of memory 1:1
+ * kernel initialization.  This maps the first 32 MBytes of memory 1:1
  * virtual to physical and more importantly sets the cache mode.
  */
 initial_mmu:
@@ -687,6 +687,12 @@ initial_mmu:
 	tlbwe	r4,r0,TLB_DATA		/* Load the data portion of the entry */
 	tlbwe	r3,r0,TLB_TAG		/* Load the tag portion of the entry */
 
+	li	r0,62			/* TLB slot 62 */
+	addis	r4,r4,SZ_16M
+	addis	r3,r3,SZ_16M
+	tlbwe	r4,r0,TLB_DATA		/* Load the data portion of the entry */
+	tlbwe	r3,r0,TLB_TAG		/* Load the tag portion of the entry */
+
 	isync
 
 	/* Establish the exception vector base
-- 
2.31.1