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SubjectRe: [PATCH] irqchip/gicv3: Add support for Range Selector (RS) feature
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Hi Marc,

On 09/16/2017 01:14 PM, Marc Zyngier wrote:
> On Fri, Sep 15 2017 at 10:08:56 am BST, Shanker Donthineni <shankerd@codeaurora.org> wrote:
>
> Hi Shanker,
>
>> A new feature Range Selector (RS) has been added to GIC specification
>> in order to support more than 16 CPUs at affinity level 0. New fields
>> are introduced in SGI system registers (ICC_SGI0R_EL1, ICC_SGI1R_EL1
>> and ICC_ASGI1R_EL1) to relax an artificial limit of 16 at level 0.
>>
>> - A new RSS field in ICC_CTLR_EL3, ICC_CTLR_EL1 and ICV_CTLR_EL1:
>> [18] - Range Selector Support (RSS)
>> 0b0 = Targeted SGIs with affinity level 0 values of 0-15 are supported.
>> 0b1 = Targeted SGIs with affinity level 0 values of 0-255 are supported.
>>
>> - A new RS field in ICC_SGI0R_EL1, ICC_SGI1R_EL1 and ICC_ASGI1R_EL1:
>> [47:44] - RangeSelector (RS) which group of 16 TargetList[n] field
>> TargetList[n] represents aff0 value ((RS*16)+n)
>> When ICC_CTLR_EL3.RSS==0 or ICC_CTLR_EL1.RSS==0, RS is RES0.
>>
>> - A new RSS field in GICD_TYPER:
>> [26] - Range Selector Support (RSS)
>> 0b0 = Targeted SGIs with affinity level 0 values of 0-15 are supported.
>> 0b1 = Targeted SGIs with affinity level 0 values of 0-255 are supported.
>>
>> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
>> ---
>> drivers/irqchip/irq-gic-v3.c | 79 ++++++++++++++++++++------------------
>> include/linux/irqchip/arm-gic-v3.h | 4 ++
>> 2 files changed, 46 insertions(+), 37 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
>> index 984c3ec..ba98c94 100644
>> --- a/drivers/irqchip/irq-gic-v3.c
>> +++ b/drivers/irqchip/irq-gic-v3.c
>> @@ -56,6 +56,7 @@ struct gic_chip_data {
>> u64 redist_stride;
>> u32 nr_redist_regions;
>> unsigned int irq_nr;
>> + bool has_rss;
>> struct partition_desc *ppi_descs[16];
>> };
>>
>> @@ -483,6 +484,9 @@ static int gic_populate_rdist(void)
>>
>> static void gic_cpu_sys_reg_init(void)
>> {
>> + int cpu = smp_processor_id();
>> + bool rss;
>> +
>> /*
>> * Need to check that the SRE bit has actually been set. If
>> * not, it means that SRE is disabled at EL2. We're going to
>> @@ -514,6 +518,15 @@ static void gic_cpu_sys_reg_init(void)
>>
>> /* ... and let's hit the road... */
>> gic_write_grpen1(1);
>> +
>> + /* GIC CPU interface has RSS capability? */
>> + rss = !!(read_sysreg_s(SYS_ICC_CTLR_EL1) & ICC_CTLR_EL1_RSS);
>> +
>> + if (gic_data.has_rss != rss)
>> + pr_info("Broken hardware, mismatch RSS, SGIs may not work\n");
>
> I disagree with this statement. The architecture allows for a non-RSS
> GIC to be matched with RSS-aware CPUs, and vice-versa. This doesn't mean
> the system is broken.
>

Yes, I agree with you, overlooked the spec. I'll fix it in v2 patch.


>> + else if ((cpu_logical_map(cpu) & 0xf0) && (!rss))
>> + pr_crit("MPIDR bits[7..4] must be zero, cpu=%d\n", cpu);
>
> That's the real "Gotcha". Finding an MPIDR_EL1.Aff0 >= 16 on any CPU if
> any of the CPUs or the distributor doesn't support RSS is an integration
> blunder. Anything else is perfectly acceptable.
>
> Unfortunately, this is not something you can decide by looking at a
> single CPU, so you'll need to accumulate some state somehow.
>

Sure, I'll enhance the validation code to check CPU AFF0 value and RSS capability
of each online CPU. Something like this.

static void gic_cpu_sys_reg_init(void)
{
....

/* Keep the RSS capability status in per_cpu variable */
per_cpu(has_rss, cpu) = !!(gic_read_ctlr() & ICC_CTLR_EL1_RSS);

/* Does it requires RSS support to send SGIs to this CPU? */
if (!MPIDR_RS(cpu_logical_map(cpu)))
return;

/* Check all the other CPUs have capable of sending SGIs to this CPU */
for_each_online_cpu(i) {
if (i == cpu)
continue;

if (!per_cpu(has_rss, i)) {
pr_crit("CPU%d doesn't support RSS, Can't send SGIs "
"to CPU%d\n", i, cpu);
continue;
}

/**
* GIC spec says, When ICC_CTLR_EL1.RSS==1 and GICD_TYPER.RSS==0,
* writing ICC_ASGI1R_EL1 register with RS != 0 is a CONSTRAINED
* UNPREDICTABLE choice of :
* - The write is ignored.
* - The RS field is treated as 0.
*/
if (!gic_data.has_rss)
pr_crit("CPU%d has RSS support but not GIC Distributor,"
" Can't send SGIs to CPU%d", i, cpu);
}
}

>> +
>> }
>>
>> static int gic_dist_supports_lpis(void)
>> @@ -554,43 +567,13 @@ static int gic_starting_cpu(unsigned int cpu)
>> return 0;
>> }
>>
>> -static u16 gic_compute_target_list(int *base_cpu, const struct cpumask *mask,
>> - unsigned long cluster_id)
>> -{
>> - int next_cpu, cpu = *base_cpu;
>> - unsigned long mpidr = cpu_logical_map(cpu);
>> - u16 tlist = 0;
>> -
>> - while (cpu < nr_cpu_ids) {
>> - /*
>> - * If we ever get a cluster of more than 16 CPUs, just
>> - * scream and skip that CPU.
>> - */
>> - if (WARN_ON((mpidr & 0xff) >= 16))
>> - goto out;
>> -
>> - tlist |= 1 << (mpidr & 0xf);
>> -
>> - next_cpu = cpumask_next(cpu, mask);
>> - if (next_cpu >= nr_cpu_ids)
>> - goto out;
>> - cpu = next_cpu;
>> -
>> - mpidr = cpu_logical_map(cpu);
>> -
>> - if (cluster_id != (mpidr & ~0xffUL)) {
>> - cpu--;
>> - goto out;
>> - }
>> - }
>> -out:
>> - *base_cpu = cpu;
>> - return tlist;
>> -}
>> -
>> #define MPIDR_TO_SGI_AFFINITY(cluster_id, level) \
>> (MPIDR_AFFINITY_LEVEL(cluster_id, level) \
>> << ICC_SGI1R_AFFINITY_## level ##_SHIFT)
>> +#define MPIDR_RS(mpidr) (((mpidr) & 0xF0) >> 4)
>> +#define MPIDR_TO_SGI_TARGETLIST(mpidr) (1 << ((mpidr) & 0xF))
>> +#define MPIDR_TO_SGI_CLUSTER_ID(mpidr) (mpidr & ~0xF)
>> +#define MPIDR_TO_SGI_RS(mpidr) (MPIDR_RS(mpidr) << ICC_SGI1R_RS_SHIFT)
>>
>> static void gic_send_sgi(u64 cluster_id, u16 tlist, unsigned int irq)
>> {
>> @@ -600,6 +583,7 @@ static void gic_send_sgi(u64 cluster_id, u16 tlist, unsigned int irq)
>> MPIDR_TO_SGI_AFFINITY(cluster_id, 2) |
>> irq << ICC_SGI1R_SGI_ID_SHIFT |
>> MPIDR_TO_SGI_AFFINITY(cluster_id, 1) |
>> + MPIDR_TO_SGI_RS(cluster_id) |
>> tlist << ICC_SGI1R_TARGET_LIST_SHIFT);
>>
>> pr_debug("CPU%d: ICC_SGI1R_EL1 %llx\n", smp_processor_id(), val);
>> @@ -620,10 +604,27 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
>> smp_wmb();
>>
>> for_each_cpu(cpu, mask) {
>> - unsigned long cluster_id = cpu_logical_map(cpu) & ~0xffUL;
>> - u16 tlist;
>> + u64 mpidr = cpu_logical_map(cpu);
>> + u64 cluster_id = MPIDR_TO_SGI_CLUSTER_ID(mpidr);
>> + u16 tlist = 0;
>> + int next_cpu;
>> +
>> + if (WARN_ON((!gic_data.has_rss) && MPIDR_RS(mpidr)))
>> + continue;
>> +
>> + /* Prepare TARGETLIST which have the same cluster_id */
>> + do {
>> + tlist |= MPIDR_TO_SGI_TARGETLIST(mpidr);
>> + next_cpu = cpumask_next(cpu, mask);
>> + if (next_cpu >= nr_cpu_ids)
>> + break;
>> +
>> + mpidr = cpu_logical_map(next_cpu);
>> + if (cluster_id != MPIDR_TO_SGI_CLUSTER_ID(mpidr))
>> + break;
>> + cpu = next_cpu;
>> + } while (true);
>
> I really dislike this. Why can't you just adapt the function we already
> have instead of making the patch pointlessly hard to review? How about
> something like this (completely untested and probably buggy, but you'll
> get the idea):
>
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index c4bec908ccea..d0539155ebae 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -603,13 +603,6 @@ static u16 gic_compute_target_list(int *base_cpu, const struct cpumask *mask,
> u16 tlist = 0;
>
> while (cpu < nr_cpu_ids) {
> - /*
> - * If we ever get a cluster of more than 16 CPUs, just
> - * scream and skip that CPU.
> - */
> - if (WARN_ON((mpidr & 0xff) >= 16))
> - goto out;
> -
> tlist |= 1 << (mpidr & 0xf);
>
> next_cpu = cpumask_next(cpu, mask);
> @@ -633,7 +626,7 @@ static u16 gic_compute_target_list(int *base_cpu, const struct cpumask *mask,
> (MPIDR_AFFINITY_LEVEL(cluster_id, level) \
> << ICC_SGI1R_AFFINITY_## level ##_SHIFT)
>
> -static void gic_send_sgi(u64 cluster_id, u16 tlist, unsigned int irq)
> +static void gic_send_sgi(u64 cluster_id, u64 rs, u16 tlist, unsigned int irq)
> {
> u64 val;
>
> @@ -641,6 +634,7 @@ static void gic_send_sgi(u64 cluster_id, u16 tlist, unsigned int irq)
> MPIDR_TO_SGI_AFFINITY(cluster_id, 2) |
> irq << ICC_SGI1R_SGI_ID_SHIFT |
> MPIDR_TO_SGI_AFFINITY(cluster_id, 1) |
> + rs << ICC_SGI1R_RS_SHIFT |
> tlist << ICC_SGI1R_TARGET_LIST_SHIFT);
>
> pr_debug("CPU%d: ICC_SGI1R_EL1 %llx\n", smp_processor_id(), val);
> @@ -662,10 +656,11 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
>
> for_each_cpu(cpu, mask) {
> unsigned long cluster_id = cpu_logical_map(cpu) & ~0xffUL;
> + u64 rs = (cpu_logical_map(cpu) >> 4) & 0xfUL;
> u16 tlist;
>
> tlist = gic_compute_target_list(&cpu, mask, cluster_id);
> - gic_send_sgi(cluster_id, tlist, irq);
> + gic_send_sgi(cluster_id, rs, tlist, irq);
> }
>
> /* Force the above writes to ICC_SGI1R_EL1 to be executed */
>
> It'd definitely look much better and would be easier to review.
>

I tried to avoid the function call overhead by changing to inline and fix one
coding bug. We're writing SGI1R register with tlist=0 when function
gic_send_sgi() fails to return valid tlist.

Anyway, I'll keep the original function and add RS support in v2 patch.

>>
>> - tlist = gic_compute_target_list(&cpu, mask, cluster_id);
>> gic_send_sgi(cluster_id, tlist, irq);
>> }
>>
>> @@ -959,6 +960,10 @@ static int __init gic_init_bases(void __iomem *dist_base,
>> goto out_free;
>> }
>>
>> + gic_data.has_rss = !!(typer & GICD_TYPER_RSS);
>> + pr_info("Distributor has %s Range Selector support\n",
>> + gic_data.has_rss ? "" : "no");
>> +
>> set_handle_irq(gic_handle_irq);
>>
>> if (IS_ENABLED(CONFIG_ARM_GIC_V3_ITS) && gic_dist_supports_lpis())
>> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
>> index 6a1f87f..eb9ff9b 100644
>> --- a/include/linux/irqchip/arm-gic-v3.h
>> +++ b/include/linux/irqchip/arm-gic-v3.h
>> @@ -68,6 +68,7 @@
>> #define GICD_CTLR_ENABLE_SS_G1 (1U << 1)
>> #define GICD_CTLR_ENABLE_SS_G0 (1U << 0)
>>
>> +#define GICD_TYPER_RSS (1U << 26)
>> #define GICD_TYPER_LPIS (1U << 17)
>> #define GICD_TYPER_MBIS (1U << 16)
>>
>> @@ -377,6 +378,7 @@
>> #define ICC_CTLR_EL1_SEIS_MASK (0x1 << ICC_CTLR_EL1_SEIS_SHIFT)
>> #define ICC_CTLR_EL1_A3V_SHIFT 15
>> #define ICC_CTLR_EL1_A3V_MASK (0x1 << ICC_CTLR_EL1_A3V_SHIFT)
>> +#define ICC_CTLR_EL1_RSS (0x1 << 18)
>> #define ICC_PMR_EL1_SHIFT 0
>> #define ICC_PMR_EL1_MASK (0xff << ICC_PMR_EL1_SHIFT)
>> #define ICC_BPR0_EL1_SHIFT 0
>> @@ -465,6 +467,8 @@
>> #define ICC_SGI1R_AFFINITY_2_SHIFT 32
>> #define ICC_SGI1R_AFFINITY_2_MASK (0xffULL << ICC_SGI1R_AFFINITY_2_SHIFT)
>> #define ICC_SGI1R_IRQ_ROUTING_MODE_BIT 40
>> +#define ICC_SGI1R_RS_SHIFT 44
>> +#define ICC_SGI1R_RS_MASK (0xfULL << ICC_SGI1R_RS_SHIFT)
>> #define ICC_SGI1R_AFFINITY_3_SHIFT 48
>> #define ICC_SGI1R_AFFINITY_3_MASK (0xffULL << ICC_SGI1R_AFFINITY_3_SHIFT)
>
> Thanks,
>
> M.
>

--
Shanker Donthineni
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

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