linux-kernel - 答复: [PATCH] tools: arm64: add registers read/write tool for arm64

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Message-ID:
 <KL1PR0601MB57734C39BCAAE623724DD501E64C2@KL1PR0601MB5773.apcprd06.prod.outlook.com>
Date: Tue, 22 Oct 2024 01:15:15 +0000
From: Rex Nie <rex.nie@...uarmicro.com>
To: Marc Zyngier <maz@...nel.org>
CC: "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
	"alexandre.torgue@...s.st.com" <alexandre.torgue@...s.st.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-stm32@...md-mailman.stormreply.com"
	<linux-stm32@...md-mailman.stormreply.com>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, Angus Chen
	<angus.chen@...uarmicro.com>
Subject:
 答复: [PATCH] tools: arm64: add registers read/write tool for arm64

HI Marc,
	Thanks for your response, I got it.
BRs
Rex

> -----邮件原件-----
> 发件人: Marc Zyngier <maz@...nel.org>
> 发送时间: 2024年10月22日 1:44
> 收件人: Rex Nie <rex.nie@...uarmicro.com>
> 抄送: mcoquelin.stm32@...il.com; alexandre.torgue@...s.st.com;
> linux-kernel@...r.kernel.org; linux-stm32@...md-mailman.stormreply.com;
> linux-arm-kernel@...ts.infradead.org; Angus Chen
> <angus.chen@...uarmicro.com>
> 主题: Re: [PATCH] tools: arm64: add registers read/write tool for arm64
> 
> External Mail: This email originated from OUTSIDE of the organization!
> Do not click links, open attachments or provide ANY information unless you
> recognize the sender and know the content is safe.
> 
> 
> On Mon, 21 Oct 2024 16:01:12 +0100,
> Rex Nie <rex.nie@...uarmicro.com> wrote:
> >
> > The reg_ctrl kernel module can read/write most aarch64 system
> > registers, including EL0/1/2/3, which is very useful when hardware
> > debuger (such as ArmDS5/trace32) is unusable.
> >
> > The primary implementation of the reg_ctrl module is as follows:
> > 1. when the core can directly access the target register, it uses
> >    the MRS/MSR instructions to read/write register.
> > 2. Otherwise, it performs an SMC call to switch to EL3, where the
> >    register read/write is completed and then return to kernel mode.
> >    I implement an OEM Service in ATF to access register at EL3,
> >    using one SMC function ID for reading and another for writing registers.
> >
> > test steps on my platform with 16x Arm Neoverse N2:
> > 1. insmod reg_ctrl.ko
> > 2. cd /sys/kernel/reg_ctrl/system/
> > 3. view the directory tree on DUT.
> > [root@...alhost system]# tree
> > .
> > ├── control
> > │   └── VNCR_EL2
> > ├── id
> > │   ├── CCSIDR_EL1
> > │   ├── CLIDR_EL1
> > │   ├── CSSELR_EL1
> > │   ├── CTR_EL0
> > │   ├── DCZID_EL0
> > │   ├── ID_AA64AFR0_EL1
> > │   ├── ID_AA64AFR1_EL1
> > │   ├── ID_AA64DFR0_EL1
> > │   ├── ID_AA64DFR1_EL1
> > │   ├── ID_AA64ISAR0_EL1
> > │   ├── ID_AA64ISAR1_EL1
> > │   ├── ID_AA64MMFR0_EL1
> > │   ├── ID_AA64MMFR1_EL1
> > │   ├── ID_AA64PFR0_EL1
> > │   └── ID_AA64PFR1_EL1
> > ├── implementation_defined
> > │   ├── IMP_CPUACTLR_EL3
> > │   ├── IMP_CPUECTLR_EL1
> > │   ├── IMP_CPUPPMCR2_EL3
> > │   ├── IMP_CPUPPMCR4_EL3
> > │   ├── IMP_CPUPPMCR5_EL3
> > │   ├── IMP_CPUPPMCR6_EL3
> > │   └── IMP_CPUPPMCR_EL3
> > └── reset
> >     └── RMR_EL3
> >
> > 4. read EL1 register on core 0:
> > [root@...alhost system]# taskset -c 0 cat id/ID_AA64PFR0_EL1
> > 0x1201111123111112
> >
> > 5. read EL3 register on core 1:
> > [root@...alhost system]# taskset -c 1 cat
> > implementation_defined/IMP_CPUPPMCR4_EL3
> > 0x2000315a10000045
> >
> > 6. set bit 1 of IMP_CPUPPMCR4_EL3 regiter on core 1:
> > [root@...alhost system]# taskset -c 1 echo 0x2000315a10000047 >
> > implementation_defined/IMP_CPUPPMCR4_EL3
> >
> > 7. check if bit 1 is set:
> > [root@...alhost system]# taskset -c 1 cat
> > implementation_defined/IMP_CPUPPMCR4_EL3
> > 0x2000315a10000047
> >
> > Signed-off-by: Rex Nie <rex.nie@...uarmicro.com>
> 
> This sort of thing has been NAKed in the past (see [1]), because it is terribly
> unsafe. I'm afraid the kernel is not a validation tool, and while I understand
> that this can be useful in extremely narrow cases, it has no place in the
> upstream kernel.
> 
> Thanks,
> 
>         M.
> 
> [1]
> https://lore.kernel.org/all/20201130174833.41315-1-rongwei.wang@linux.a
> libaba.com/
> 
> --
> Without deviation from the norm, progress is not possible.