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Re: [Qemu-devel] [PATCH] target-arm: Implement AArch64 OSLSR_EL1 sysreg


From: Davorin Mista
Subject: Re: [Qemu-devel] [PATCH] target-arm: Implement AArch64 OSLSR_EL1 sysreg dummy
Date: Wed, 23 Sep 2015 12:12:04 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0



On 09/23/2015 09:07 AM, Peter Maydell wrote:
On 22 September 2015 at 11:35, Davorin Mista <address@hidden> wrote:
Define a dummy version of the AArch64 OSLAR_EL1 system register

Should read "OSLSR_EL1" :-)

Yes, sorry about that :)


which just ignores reads.
Linux reads from this register during its suspend/resume procedure.

Signed-off-by: Davorin Mista <address@hidden>

---
  target-arm/helper.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/target-arm/helper.c b/target-arm/helper.c
index 454d666..8431181 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -3085,6 +3085,10 @@ static const ARMCPRegInfo debug_cp_reginfo[] = {
      { .name = "OSLAR_EL1", .state = ARM_CP_STATE_BOTH,
        .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 1, .crm = 0, .opc2 = 4,
        .access = PL1_W, .type = ARM_CP_NOP },
+    /* We define a dummy OSLSR_EL1, because Linux reads from it. */
+    { .name = "OSLSR_EL1", .state = ARM_CP_STATE_BOTH,
+      .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 1, .crm = 1, .opc2 = 4 ,
+      .access = PL1_R, .type = ARM_CP_NOP },
      /* Dummy OSDLR_EL1: 32-bit Linux will read this */
      { .name = "OSDLR_EL1", .state = ARM_CP_STATE_BOTH,
        .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 1, .crm = 3, .opc2 = 4,
--

I think we need to do better than reads-as-zero here if we're going
to implement this. The value read here should be 0b10x0, where the
value of 'x' is 1 on reset and is controlled by what is written to
the OSLAR_EL1.

This should be pretty straightforward to implement, we just need some
state for the OSLSR, implement OSLSR as a RO register backed by the
state field, and change OSLAR to have a write-function which alters
the OSLSR state field appropriately depending on what's written.

Okay, so we'd add a writefn for OSLAR_EL1, and a readfn for OSLSR_EL1.

Where do you suggest we keep the OSLSR state? Directly in the ARMCPU struct? As far as I can tell it's the first register from the PTM-A9 block. None of the other debug registers have read/write functions so far.

Also, what type should the register be? Out of the available ARM_CP_xx types I'm not sure which one(s) apply.

Thanks,
Davorin


thanks
-- PMM




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