Re: [PATCH] Fix for TLB errata on early Xilinx Virtex-II Pro silicon

Grant Likely wrote:

quoted

Early versions of the Xilinx Virtex-II Pro have a TLB errata where
only even numbered TLB entries work correctly.  Occurs on chips where
PVR == 0x20010820 || 0x20010860

See Record #14052, solution #12 in the Xilinx answers database
http://www.xilinx.com/xlnx/xil_ans_display.jsp?getPagePath=14052

This patch adds a config option to use only even TLB entries on the 
V2Pro
It also makes a trivial change to the Kconfig so that Xilinx options 
depend
on VIRTEX_II_PRO instead of XILINX_ML300

Signed-off-by: Grant Likely <redacted>
---

 arch/ppc/kernel/head_4xx.S     |   11 +++++++++++
 arch/ppc/platforms/4xx/Kconfig |   28 ++++++++++++++++++++++------
 2 files changed, 33 insertions(+), 6 deletions(-)

322a82cd190a777e4ebe728cad2a2a3759039260

diff --git a/arch/ppc/kernel/head_4xx.S b/arch/ppc/kernel/head_4xx.S
--- a/arch/ppc/kernel/head_4xx.S
+++ b/arch/ppc/kernel/head_4xx.S

@@ -769,7 +769,11 @@ finish_tlb_load:
        /* load the next available TLB index.
        */
        lwz     r9, tlb_4xx_index@l(0)
+#if defined(CONFIG_VIRTEX_II_PRO_TLB_FIX)
+       addi    r9, r9, 2
+#else
        addi    r9, r9, 1
+#endif
        andi.   r9, r9, (PPC4XX_TLB_SIZE-1)
        stw     r9, tlb_4xx_index@l(0)

I would also fix the comment in this file
(it has nothing to do with the TLB fix but...):

@@ -915,10 +919,10 @@ initial_mmu:
    mtspr    SPRN_PID,r0
    sync

-    /* Configure and load two entries into TLB slots 62 and 63.
-     * In case we are pinning TLBs, these are reserved in by the
+    /* Configure and load an entry into TLB slot 63.
+     * In case we are pinning TLBs, it is reserved in by the
     * other TLB functions.  If not reserving, then it doesn't
-     * matter where they are loaded.
+     * matter where it is loaded.
     */
    clrrwi    r4,r4,10        /* Mask off the real page number */
    ori    r4,r4,(TLB_WR | TLB_EX)    /* Set the write and execute 

bits */

quoted

@@ -926,7 +930,14 @@ initial_mmu:
        clrrwi  r3,r3,10                /* Mask off the effective 

page number */        ori     r3,r3,(TLB_VALID | TLB_PAGESZ(PAGESZ_16M))

+#if defined(CONFIG_VIRTEX_II_PRO_TLB_FIX)
+       /* Odd numbered TLB slots are broken on Xilinx V2Pro processors
+        * where PVR = 20010820 | 20010860
+        */
+        li      r0,62                    /* TLB slot 62 */
+#else
         li      r0,63                    /* TLB slot 63 */
+#endif

        tlbwe   r4,r0,TLB_DATA          /* Load the data portion of 
the entry */        tlbwe   r3,r0,TLB_TAG           /* Load the tag 
portion of the entry */

diff --git a/arch/ppc/platforms/4xx/Kconfig 

b/arch/ppc/platforms/4xx/Kconfig

--- a/arch/ppc/platforms/4xx/Kconfig
+++ b/arch/ppc/platforms/4xx/Kconfig

@@ -161,11 +161,6 @@ config IBM_OCP
        depends on ASH || BAMBOO || BUBINGA || CPCI405 || EBONY || 

EP405 || LUAN || OCOTEA || REDWOOD_5 || REDWOOD_6 || SYCAMORE || WALNUT
        default y

-config XILINX_OCP
-       bool
-       depends on XILINX_ML300
-       default y
-
 config IBM_EMAC4
        bool
        depends on 440GX || 440SP

@@ -201,6 +196,27 @@ config VIRTEX_II_PRO
        depends on XILINX_ML300
        default y

+config VIRTEX_II_PRO_TLB_FIX
+       bool "Virtex-II Pro TLB bugfix"
+       depends on VIRTEX_II_PRO
+       default n
+       help
+         Early versions of the Xilinx Virtex-II Pro have a TLB 

errata where
+         only even numbered TLB entries work correctly.  Say Y here if
+         PVR == 0x20010820 || 0x20010860, or if your board crashes 
early
+         after enabling the MMU
+
+         See Record #14052, solution #12 in the Xilinx answers database
+         
http://www.xilinx.com/xlnx/xil_ans_display.jsp?getPagePath=14052
+
+         It is safe to say Y here, but there is a performance impact.
+         Say N if unsure.
+
+config XILINX_OCP
+       bool
+       depends on VIRTEX_II_PRO
+       default y
+
 config STB03xxx
        bool
        depends on REDWOOD_5 || REDWOOD_6

@@ -208,7 +224,7 @@ config STB03xxx

 config EMBEDDEDBOOT
        bool
-       depends on EP405 || XILINX_ML300
+       depends on EP405 || VIRTEX_II_PRO
        default y

 config IBM_OPENBIOS

I would drop the last chunk.
I agree that VIRTEX_II_PRO_TLB_FIX and XILINX_OCP should depend on the
chip (VIRTEX_II_PRO), but using EMBEDDEDBOOT or, say, U-Boot is at least
board specific. Well, even the same board can use different bootloaders,
but tying together EMBEDDEDBOOT and VIRTEX_II_PRO is even worse IMO.

Otherwise the patch looks OK.

These changes to head_4xx.S were tested OK on ML300:
in both cases (odd numbered TLB slots used or not) there were no 
problems.
(For some unknown reason my ML300 doesn't need this workaround though
'cat /proc/cpuinfo' gets "revision        : 8.32 (pvr 2001 0820)")

Thanks,
Andrei

quoted

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