Re: [PATCH v2] irqchip: gic-v3: Extend collection table

[Marc Zyngier]

On Fri, 09 Jun 2023 11:02:04 +0100,
wangwudi <wangwudi@xxxxxxxxxxxxx> wrote:
> 
> Hi Marc,
> 
> 在 2023/6/9 17:24, wangwudi 写道:
> > 
> > 
> > -----邮件原件-----
> > 发件人: Marc Zyngier [mailto:maz@xxxxxxxxxx] 
> > 发送时间: 2023年6月8日 16:10
> > 收件人: wangwudi <wangwudi@xxxxxxxxxxxxx>
> > 抄送: linux-kernel@xxxxxxxxxxxxxxx; liaochang (A) <liaochang1@xxxxxxxxxx>; Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > 主题: Re: [PATCH v2] irqchip: gic-v3: Extend collection table
> > 
> > On Wed, 07 Jun 2023 10:45:13 +0100,
> > wangwudi <wangwudi@xxxxxxxxxxxxx> wrote:
> >>
> >> Only single level table is supported to the collection table, and only 
> >> one page is allocated.
> >>
> >> Extend collection table to support more CPUs:
> >> 1. Recalculate the page number of collection table based on the number 
> >> of CPUs.
> >> 2. Add 2 level tables to collection table.
> >> 3. Add GITS_TYPER_CIDBITS macros.
> >>
> >> It is noticed in an internal simulation research:
> >> - the page_size of collection table is 4 KB
> >> - the entry_size of collection table is 16 Byte
> >> - with 512 CPUs
> >>
> >> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> >> Cc: Marc Zyngier <maz@xxxxxxxxxx>
> >> Signed-off-by: wangwudi <wangwudi@xxxxxxxxxxxxx>
> >> ---
> >>
> >> ChangeLog:
> >> v1-->v2:
> >> 	1. Support 2 level table
> >> 	2. Rewrite the commit log
> >>
> >>  drivers/irqchip/irq-gic-v3-its.c   | 62 ++++++++++++++++++++++++++++++--------
> >>  include/linux/irqchip/arm-gic-v3.h |  3 ++
> >>  2 files changed, 53 insertions(+), 12 deletions(-)
> >>
> >> diff --git a/drivers/irqchip/irq-gic-v3-its.c 
> >> b/drivers/irqchip/irq-gic-v3-its.c
> >> index 0ec2b1e1df75..573ef26ad449 100644
> >> --- a/drivers/irqchip/irq-gic-v3-its.c
> >> +++ b/drivers/irqchip/irq-gic-v3-its.c
> >> @@ -126,6 +126,7 @@ struct its_node {
> >>  #define is_v4(its)		(!!((its)->typer & GITS_TYPER_VLPIS))
> >>  #define is_v4_1(its)		(!!((its)->typer & GITS_TYPER_VMAPP))
> >>  #define device_ids(its)		(FIELD_GET(GITS_TYPER_DEVBITS, (its)->typer) + 1)
> >> +#define collection_ids(its)	(FIELD_GET(GITS_TYPER_CIDBITS, (its)->typer) + 1)
> >>  
> >>  #define ITS_ITT_ALIGN		SZ_256
> >>  
> >> @@ -2626,6 +2627,10 @@ static int its_alloc_tables(struct its_node *its)
> >>  			indirect = its_parse_indirect_baser(its, baser, &order,
> >>  							    ITS_MAX_VPEID_BITS);
> >>  			break;
> >> +		case GITS_BASER_TYPE_COLLECTION:
> >> +			indirect = its_parse_indirect_baser(its, baser, &order,
> >> +							    order_base_2(num_possible_cpus()));
> >> +			break;
> > 
> > Nice try, but no. See below.
> > 
> >>  		}
> >>  
> >>  		err = its_setup_baser(its, baser, cache, shr, order, indirect); @@ 
> >> -3230,18 +3235,6 @@ static void its_cpu_init_collection(struct its_node *its)
> >>  	its_send_invall(its, &its->collections[cpu]);  }
> >>  
> >> -static void its_cpu_init_collections(void) -{
> >> -	struct its_node *its;
> >> -
> >> -	raw_spin_lock(&its_lock);
> >> -
> >> -	list_for_each_entry(its, &its_nodes, entry)
> >> -		its_cpu_init_collection(its);
> >> -
> >> -	raw_spin_unlock(&its_lock);
> >> -}
> >> -
> >>  static struct its_device *its_find_device(struct its_node *its, u32 
> >> dev_id)  {
> >>  	struct its_device *its_dev = NULL, *tmp; @@ -3316,6 +3309,51 @@ 
> >> static bool its_alloc_table_entry(struct its_node *its,
> >>  	return true;
> >>  }
> >>  
> >> +static bool its_alloc_collection_table(struct its_node *its, struct 
> >> +its_baser *baser) {
> >> +	int cpu = smp_processor_id();
> >> +	int cpu_ids = 16;
> >> +
> >> +	if (its->typer & GITS_TYPER_CIL)
> >> +		cpu_ids = collection_ids(its);
> >> +
> >> +	if (!(ilog2(cpu) < cpu_ids)) {
> >> +		pr_warn("ITS: CPU%d out of Collection ID range for %dbits", cpu, cpu_ids);
> >> +		return false;
> >> +	}
> >> +
> >> +	if (!its_alloc_table_entry(its, baser, cpu)) {
> >> +		pr_warn("ITS: CPU%d failed to allocate collection l2 table", cpu);
> >> +		return false;
> >> +	}
> >> +
> >> +	return true;
> >> +}
> >> +
> >> +static bool its_cpu_init_collections(void) {
> >> +	struct its_node *its;
> >> +	struct its_baser *baser;
> >> +
> >> +	raw_spin_lock(&its_lock);
> >> +
> >> +	list_for_each_entry(its, &its_nodes, entry) {
> >> +		baser = its_get_baser(its, GITS_BASER_TYPE_COLLECTION);
> >> +		if (!baser) {
> >> +			raw_spin_unlock(&its_lock);
> >> +			return false;
> >> +		}
> > 
> > This looks wrong. ITSs that have a non-zero HCC field may not need
> > memory to back their collections at all, such as GIC500. There may
> > not even be a BASERn register holding the memory.
> > 
> > So this patch more or less *guarantees* to break most
> > implementation that are more than 5 year old.
> >
> 
> For the collection table, if the HCC field is not zero, neither
> l1-table nor l2-table table is allocated. How do you think?

What do I think? I've already said what I think, right under the 4
lines of code that break anything with a GIC500.

	M.

-- 
Without deviation from the norm, progress is not possible.