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SubjectRe: [PATCH 2/2] irqchip/apple-aic: Add support for A7-A11 SoCs
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On 12.07.2022 20:52, Sven Peter wrote:
> marcan probably has to review this in detail but two comments from me:
>
> On Tue, Jul 12, 2022, at 18:09, Konrad Dybcio wrote:
>> Add support for A7-A11 SoCs by if-ing out some features only present on
>> A12 & newer (UNCORE2 registers) or M1 & newer (EL2 registers - the
>> older SoCs don't implement EL2).
>>
>> Also, annotate IPI regs support (A11 and newer*) so that the driver can
>> tell whether the SoC supports these (they are written to even if fast
>> IPI is disabled, when the registers are there of course).
>>
>> *A11 is supposed to use this feature, but it is currently not working.
>> That said, it is not yet necessary, especially with only one core up,
>> and it works a-ok using the same featureset as earlier SoCs.
>>
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@somainline.org>
>> ---
>> drivers/irqchip/irq-apple-aic.c | 54 +++++++++++++++++++++++----------
>> 1 file changed, 38 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-apple-aic.c b/drivers/irqchip/irq-apple-aic.c
>> index 12dd48727a15..36f4b52addc2 100644
>> --- a/drivers/irqchip/irq-apple-aic.c
>> +++ b/drivers/irqchip/irq-apple-aic.c
>> @@ -245,7 +245,10 @@ struct aic_info {
>> u32 die_stride;
>>
>> /* Features */
>> + bool el2_regs;
>> bool fast_ipi;
>> + bool ipi_regs;
>> + bool uncore2_regs;
>
> I don't quite understand the difference between fast_ipi and ipi_regs.
> Don't we always have fast_ipi suppport when those regs are available?
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/irqchip/irq-apple-aic.c?h=next-20220712#n532

Both cases invoke accessing IPI regs, and there was a ipi/no-ipi variant
before, so I didn't want to mess with that.


>
>> };
>>
>> static const struct aic_info aic1_info = {
>> @@ -261,7 +264,10 @@ static const struct aic_info aic1_fipi_info = {
>> .event = AIC_EVENT,
>> .target_cpu = AIC_TARGET_CPU,
>>
>> + .el2_regs = true,
>> .fast_ipi = true,
>> + .ipi_regs = true,
>> + .uncore2_regs = true,
>> };
>>
>> static const struct aic_info aic2_info = {
>> @@ -269,7 +275,10 @@ static const struct aic_info aic2_info = {
>>
>> .irq_cfg = AIC2_IRQ_CFG,
>>
>> + .el2_regs = true,
>> .fast_ipi = true,
>> + .ipi_regs = true,
>> + .uncore2_regs = true,
>> };
>>
>> static const struct of_device_id aic_info_match[] = {
>> @@ -452,6 +461,9 @@ static unsigned long aic_fiq_get_idx(struct irq_data *d)
>>
>> static void aic_fiq_set_mask(struct irq_data *d)
>> {
>> + if (!aic_irqc->info.el2_regs)
>> + return;
>> +
>> /* Only the guest timers have real mask bits, unfortunately. */
>> switch (aic_fiq_get_idx(d)) {
>> case AIC_TMR_EL02_PHYS:
>> @@ -469,6 +481,9 @@ static void aic_fiq_set_mask(struct irq_data *d)
>>
>> static void aic_fiq_clear_mask(struct irq_data *d)
>> {
>> + if (!aic_irqc->info.el2_regs)
>> + return;
>> +
>> switch (aic_fiq_get_idx(d)) {
>> case AIC_TMR_EL02_PHYS:
>> sysreg_clear_set_s(SYS_IMP_APL_VM_TMR_FIQ_ENA_EL2, 0,
>> VM_TMR_FIQ_ENABLE_P);
>> @@ -524,12 +539,14 @@ static void __exception_irq_entry
>> aic_handle_fiq(struct pt_regs *regs)
>> * we check for everything here, even things we don't support yet.
>> */
>>
>> - 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 (aic_irqc->info.ipi_regs) {
>> + 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);
>> + }
>> }
>> }
>
> This is a pretty hot path and the use_fast_ipi check uses the jump label support
> (static_branch_likely, static_branch_enable) to avoid dereferencing memory here.
> We'll probably want the same for the other features.
>
> For this branch here the else can probably just be removed: I think that's
> a leftover from when this driver just didn't support fastipi at all even
> when the registers were available.
If there's no use for non-fast-ipi paths, perhaps they can just be removed?
That could simplify the fast_ipi/ipi_regs situation.

Konrad
>
>
>
> Sven
>

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