Re: [PATCH RESEND 2/3] irqchip/apple-aic: Only access IPI sysregs when use_fast_ipi is true

[Nick Chan <towinchenmi@gmail.com>]

On 29/8/2024 21:08, Thomas Gleixner wrote:
> On Thu, Aug 29 2024 at 19:02, Nick Chan wrote:
>> Starting from the A11 (T8015) SoC, Apple introuced system registers for
>> fast IPI and UNCORE PMC control. These sysregs do not exist on earlier
>> A7-A10 SoCs and trying to access them results in an instant crash.
>>
>> Restrict sysreg access within the AIC driver to configurations where
>> use_fast_ipi is true to allow AIC to function properly on A7-A10 SoCs.
> 
> use_fast_ipi is an implementation detail and does not mean anything
> here. It's sufficient to say:
> 
>    Only access system registers on SoCs which provide them.
> 
> Hmm?
Seems like a good idea. Will be in v2. Though if the commit message
is that generic, do you think it's correct to squash the third patch
into this commit? It is also preventing sysreg access on SoC that
do not provide them.

> 
>> While at it, remove the IPI-always-ack path on aic_handle_fiq.
> 
> It's not while at it. It's part of handling this correctly.
In v2 it will be mentioned as as part of the sysreg access restriction.

> 
>> If we are able to reach there, we are on an IPI-capable system and
>> should be using one of the IPI-capable compatibles, anyway.
> 
> 'we' can't reach that code ever.
> 
> https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#changelog
Acked. In v2 the commit message will not impersonate the code anymore.

> 
> 
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@somainline.org>
>> Signed-off-by: Nick Chan <towinchenmi@gmail.com>
> 
> This Signed-off-by chain is invalid. If Konrad authored the patch then
> you need to have a 'From: Konrad ...' line at the top of the change log.
> 
> If you worked together on this then this needs a Co-developed-by
> tag. See Documentation/process/...
This patch was entirely made by Konrad, but now that changes are requested,
it will be a Co-developed-by in v2.

> 
>>  
>> -	if (read_sysreg_s(SYS_IMP_APL_IPI_SR_EL1) & IPI_SR_PENDING) {
>> -		if (static_branch_likely(&use_fast_ipi)) {
>> -			aic_handle_ipi(regs);
>> -		} else {
>> -			pr_err_ratelimited("Fast IPI fired. Acking.\n");
>> -			write_sysreg_s(IPI_SR_PENDING, SYS_IMP_APL_IPI_SR_EL1);
>> -		}
>> +	if (static_branch_likely(&use_fast_ipi) &&
>> +	    (read_sysreg_s(SYS_IMP_APL_IPI_SR_EL1) & IPI_SR_PENDING)) {
>> +		aic_handle_ipi(regs);
>>  	}
>>  
>>  	if (TIMER_FIRING(read_sysreg(cntp_ctl_el0)))
>> @@ -574,8 +571,9 @@ static void __exception_irq_entry aic_handle_fiq(struct pt_regs *regs)
>>  					  AIC_FIQ_HWIRQ(irq));
>>  	}
>>  
>> -	if (FIELD_GET(UPMCR0_IMODE, read_sysreg_s(SYS_IMP_APL_UPMCR0_EL1)) == UPMCR0_IMODE_FIQ &&
>> -			(read_sysreg_s(SYS_IMP_APL_UPMSR_EL1) & UPMSR_IACT)) {
>> +	if (static_branch_likely(&use_fast_ipi) &&
>> +	    (FIELD_GET(UPMCR0_IMODE, read_sysreg_s(SYS_IMP_APL_UPMCR0_EL1)) == UPMCR0_IMODE_FIQ) &&
>> +	    (read_sysreg_s(SYS_IMP_APL_UPMSR_EL1) & UPMSR_IACT)) {
>>  		/* Same story with uncore PMCs */
>>  		pr_err_ratelimited("Uncore PMC FIQ fired. Masking.\n");
>>  		sysreg_clear_set_s(SYS_IMP_APL_UPMCR0_EL1, UPMCR0_IMODE,
>> @@ -811,7 +809,8 @@ static int aic_init_cpu(unsigned int cpu)
>>  	/* Mask all hard-wired per-CPU IRQ/FIQ sources */
>>  
>>  	/* Pending Fast IPI FIQs */
>> -	write_sysreg_s(IPI_SR_PENDING, SYS_IMP_APL_IPI_SR_EL1);
>> +	if (static_branch_likely(&use_fast_ipi))
>> +		write_sysreg_s(IPI_SR_PENDING, SYS_IMP_APL_IPI_SR_EL1);
>>  
>>  	/* Timer FIQs */
>>  	sysreg_clear_set(cntp_ctl_el0, 0, ARCH_TIMER_CTRL_IT_MASK);
>> @@ -832,8 +831,9 @@ static int aic_init_cpu(unsigned int cpu)
>>  			   FIELD_PREP(PMCR0_IMODE, PMCR0_IMODE_OFF));
>>  
>>  	/* Uncore PMC FIQ */
>> -	sysreg_clear_set_s(SYS_IMP_APL_UPMCR0_EL1, UPMCR0_IMODE,
>> -			   FIELD_PREP(UPMCR0_IMODE, UPMCR0_IMODE_OFF));
>> +	if (static_branch_likely(&use_fast_ipi))
>> +		sysreg_clear_set_s(SYS_IMP_APL_UPMCR0_EL1, UPMCR0_IMODE,
>> +				   FIELD_PREP(UPMCR0_IMODE, UPMCR0_IMODE_OFF));
> 
> Please see the bracket rules in the tip maintainers doc.
Acked. Brackets will be added to function references in commit message
of v2.

> 
> Thanks,
> 
>         tglx

Nick Chan