linux-kernel - Re: [PATCH v3 1/8] arm64/sysreg: Add definitions for immediate versions of MSR ALLINT

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Date: Mon, 3 Jun 2024 11:26:39 +0800
From: "Liao, Chang" <liaochang1@...wei.com>
To: Mark Brown <broonie@...nel.org>
CC: Mark Rutland <mark.rutland@....com>, <catalin.marinas@....com>,
	<will@...nel.org>, <maz@...nel.org>, <oliver.upton@...ux.dev>,
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	<kvmarm@...ts.linux.dev>
Subject: Re: [PATCH v3 1/8] arm64/sysreg: Add definitions for immediate
 versions of MSR ALLINT

Hi, Mark

在 2024/5/7 22:52, Mark Brown 写道:
> On Tue, May 07, 2024 at 03:41:08PM +0800, Liao, Chang wrote:
>> 在 2024/5/6 23:15, Mark Brown 写道:
>>> On Fri, May 03, 2024 at 05:00:49PM +0100, Mark Rutland wrote:
> 
>>>> +#define set_pstate_allint(x)           asm volatile(SET_PSTATE_ALLINT(x))
> 
>>> Hrm, those helpers are not ideally discoverable, partly due to the
>>> system register description for ALLINT not providing any references to
>>> this being a general scheme (which is fixable there) and partly due to
> 
>> Based on the Arm ISA reference manual, the instruction accessing the ALLINT
>> field of PSTATE uses the following encoding:
> 
> I'm not saying the suggestion is wrong, I'm saying that between the ARM
> and the way the code is written the helpers aren't as discoverable as
> they should be, like I say from a code point of view that's mainly
> because...
> 
>>                     op0  op1   CRn    CRm    op2
>> MSR ALLINT, #<imm>  0b00 0b001 0b0100 0b000x 0b000
> 
> ...we only have the encoding for the MSR and don't mention the letters
> 'msr' anywhere.  We should improve that to say what we're encoding in
> the code (in general I'd say that's true for any __emit_inst(), not just
> these ones).

Oh, I apologize any confusion in my previous message.

Mark, Is your concern is that the series of pstate related macro name in
sysregs.h are lack of self-explanatory nature, which make it diffuclt to
understand their functionality and purpose? If so, I daft some alternative
macro names in the code below, looking forward to your feedback, or if you
have any proposal for making these helpers discoverable.

----8<----
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 643e2ad73cbd..4f514bdfb1bd 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -90,7 +90,7 @@
  */
 #define pstate_field(op1, op2)         ((op1) << Op1_shift | (op2) << Op2_shift)
 #define PSTATE_Imm_shift               CRm_shift
-#define SET_PSTATE(x, r)               __emit_inst(0xd500401f | PSTATE_ ## r | ((!!x) << PSTATE_Imm_shift))
+#define MSR_PSTATE_ENCODE(x, r)                __emit_inst(0xd500401f | PSTATE_ ## r | ((!!x) << PSTATE_Imm_shift))

 #define PSTATE_PAN                     pstate_field(0, 4)
 #define PSTATE_UAO                     pstate_field(0, 3)
@@ -99,18 +99,18 @@
 #define PSTATE_TCO                     pstate_field(3, 4)
 #define PSTATE_ALLINT                  pstate_field(1, 0)

-#define SET_PSTATE_PAN(x)              SET_PSTATE((x), PAN)
-#define SET_PSTATE_UAO(x)              SET_PSTATE((x), UAO)
-#define SET_PSTATE_SSBS(x)             SET_PSTATE((x), SSBS)
-#define SET_PSTATE_DIT(x)              SET_PSTATE((x), DIT)
-#define SET_PSTATE_TCO(x)              SET_PSTATE((x), TCO)
-#define SET_PSTATE_ALLINT(x)           SET_PSTATE((x), ALLINT)
-
-#define set_pstate_pan(x)              asm volatile(SET_PSTATE_PAN(x))
-#define set_pstate_uao(x)              asm volatile(SET_PSTATE_UAO(x))
-#define set_pstate_ssbs(x)             asm volatile(SET_PSTATE_SSBS(x))
-#define set_pstate_dit(x)              asm volatile(SET_PSTATE_DIT(x))
-#define set_pstate_allint(x)           asm volatile(SET_PSTATE_ALLINT(x))
+#define MSR_PSTATE_PAN(x)              MSR_PSTATE_ENCODE((x), PAN)
+#define MSR_PSTATE_UAO(x)              MSR_PSTATE_ENCODE((x), UAO)
+#define MSR_PSTATE_SSBS(x)             MSR_PSTATE_ENCODE((x), SSBS)
+#define MSR_PSTATE_DIT(x)              MSR_PSTATE_ENCODE((x), DIT)
+#define MSR_PSTATE_TCO(x)              MSR_PSTATE_ENCODE((x), TCO)
+#define MSR_PSTATE_ALLINT(x)           MSR_PSTATE_ENCODE((x), ALLINT)
+
+#define msr_pstate_pan(x)              asm volatile(MSR_PSTATE_PAN(x))
+#define msr_pstate_uao(x)              asm volatile(MSR_PSTATE_UAO(x))
+#define msr_pstate_ssbs(x)             asm volatile(MSR_PSTATE_SSBS(x))
+#define msr_pstate_dit(x)              asm volatile(MSR_PSTATE_DIT(x))
+#define msr_pstate_allint(x)           asm volatile(MSR_PSTATE_ALLINT(x))
---->8----

Thanks.

-- 
BR
Liao, Chang