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Re: [PATCH 26/35] target/arm: Implement FEAT_NV2 redirection of sysregs


From: Richard Henderson
Subject: Re: [PATCH 26/35] target/arm: Implement FEAT_NV2 redirection of sysregs to RAM
Date: Tue, 9 Jan 2024 19:40:59 +1100
User-agent: Mozilla Thunderbird

On 1/5/24 03:23, Peter Maydell wrote:
On Wed, 27 Dec 2023 at 23:55, Richard Henderson
<richard.henderson@linaro.org> wrote:

On 12/18/23 22:32, Peter Maydell wrote:
+    if (s->nv && s->nv2 && ri->nv2_redirect_offset) {

Again, s->nv test is redundant.

Fixed, thanks.

+        /*
+         * Some registers always redirect to memory; some only do so if
+         * HCR_EL2.NV1 is 0, and some only if NV1 is 1 (these come in
+         * pairs which share an offset; see the table in R_CSRPQ).
+         */
+        if (ri->nv2_redirect_offset & NV2_REDIR_NV1) {
+            nv2_mem_redirect = s->nv1;
+        } else if (ri->nv2_redirect_offset & NV2_REDIR_NO_NV1) {
+            nv2_mem_redirect = !s->nv1;
+        } else {
+            nv2_mem_redirect = true;
+        }

I wondered if it would be clearer with the "both" case having both bits set.  
While I see
that the first defined offset is 0x20, offset 0x00 is still reserved and 
*could* be used.
At which point ri->nv2_redirect_offset would need a non-zero value for a zero 
offset.

Maybe clearer as

      nv2_mem_redirect = (ri->nv2_redirect_offset &
                          (s->nv1 ? NV2_REDIR_NV1_1 : NV2_REDIR_NV1_0));

?

This is more verbose for the (common?) case of redirect regardless of nv1, so 
maybe not.

Yes, my motivation for the notation I used is that I wanted to
make the specification of the cpreg structs in the common case
simple and not too long-winded. If offset 0 does ever get
allocated, we'll have to come back and revisit this. But
new entries clearly seem to be being allocated at the other
end of the table, so I think our chances are good...

+        if (s->nv2_mem_be) {
+            mop |= MO_BE;
+        }

MO_BSWAP is host dependent -- needs

      mop |= (s->nv2_mem_be ? MO_BE : MO_LE);

Fixed.

With those two fixes, can I have a reviewed-by? This is the
only patch without one, and all the fixes seem to me like
very minor things not worth sending out a full v2 for.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~



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