Since device IDs are extremely sparse, the single, a.k.a flat table is not sufficient for the following two reasons.
1) According to ARM-GIC spec, ITS hw can access maximum of 256(pages)* 64K(pageszie) bytes. In the best case, it supports upto DEVid=21 sparse with minimum device table entry size 8bytes. 2) The maximum memory size that is possible without memblock depends on MAX_ORDER. 4MB on 4K page size kernel with default MAX_ORDER, so it supports DEVid range 19bits. The two-level device table feature brings us two advantages, the first is a very high possibility of supporting upto 32bit sparse, and the second one is the best utilization of memory allocation. The feature is enabled automatically during driver probe if a single ITS page is not adequate for flat table and the hardware is capable of two-level table walk. Signed-off-by: Shanker Donthineni <shank...@codeaurora.org> --- This patch is based on Marc Zyngier's branch https://git.kernel.org/cgit/linux/kernel/git/maz/arm-platforms.git/log/?h=irq/irqchip-4.7 I have tested the Indirection feature on Qualcomm Technologies QDF2XXX server platform. Changes since v1: Most of this patch has been rewritten after refactoring its_alloc_tables(). Always enable device two-level if the memory requirement is more than PAGE_SIZE. Fixed the coding bug that breaks on the BE machine. Edited the commit text. drivers/irqchip/irq-gic-v3-its.c | 100 ++++++++++++++++++++++++++++++++------- 1 file changed, 83 insertions(+), 17 deletions(-) diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c index b23e00c..27be792 100644 --- a/drivers/irqchip/irq-gic-v3-its.c +++ b/drivers/irqchip/irq-gic-v3-its.c @@ -938,6 +938,18 @@ retry_baser: return 0; } +/** + * Find out whether an implemented baser register supports a single, flat table + * or a two-level table by reading bit offset at '62' after writing '1' to it. + */ +static u64 its_baser_check_indirect(struct its_baser *baser) +{ + u64 val = GITS_BASER_InnerShareable | GITS_BASER_WaWb; + + writeq_relaxed(val | GITS_BASER_INDIRECT, baser->hwreg); + return (readq_relaxed(baser->hwreg) & GITS_BASER_INDIRECT); +} + static int its_alloc_tables(const char *node_name, struct its_node *its) { u64 typer = readq_relaxed(its->base + GITS_TYPER); @@ -964,6 +976,7 @@ static int its_alloc_tables(const char *node_name, struct its_node *its) u64 entry_size = GITS_BASER_ENTRY_SIZE(val); int order = get_order(psz); struct its_baser *baser = its->tables + i; + u64 indirect = 0; if (type == GITS_BASER_TYPE_NONE) continue; @@ -977,17 +990,27 @@ static int its_alloc_tables(const char *node_name, struct its_node *its) * Allocate as many entries as required to fit the * range of device IDs that the ITS can grok... The ID * space being incredibly sparse, this results in a - * massive waste of memory. + * massive waste of memory if two-level device table + * feature is not supported by hardware. * * For other tables, only allocate a single page. */ if (type == GITS_BASER_TYPE_DEVICE) { - /* - * 'order' was initialized earlier to the default page - * granule of the the ITS. We can't have an allocation - * smaller than that. If the requested allocation - * is smaller, round up to the default page granule. - */ + if ((entry_size << ids) > psz) + indirect = its_baser_check_indirect(baser); + + if (indirect) { + /* + * The size of the lvl2 table is equal to ITS + * page size which is 'psz'. For computing lvl1 + * table size, subtract ID bits that sparse + * lvl2 table from 'ids' which is reported by + * ITS hardware times lvl1 table entry size. + */ + ids -= ilog2(psz / entry_size); + entry_size = GITS_LVL1_ENTRY_SIZE; + } + order = max(get_order(entry_size << ids), order); if (order >= MAX_ORDER) { order = MAX_ORDER - 1; @@ -997,7 +1020,7 @@ static int its_alloc_tables(const char *node_name, struct its_node *its) } } - err = its_baser_setup(its, baser, order, 0); + err = its_baser_setup(its, baser, order, indirect); if (err < 0) { its_free_tables(its); return err; @@ -1187,10 +1210,60 @@ static struct its_baser *its_get_baser(struct its_node *its, u32 type) return NULL; } +static bool its_alloc_device_table(struct its_node *its, u32 dev_id) +{ + struct its_baser *baser; + struct page *page; + u32 entry_size, idx; + u64 *table; + + baser = its_get_baser(its, GITS_BASER_TYPE_DEVICE); + + /* Don't allow 'dev_id' that exceeds ITS hardware limit */ + if (!baser && (ilog2(dev_id) >= its->device_ids)) + return false; + + /* Don't allow 'dev_id' that exceeds single, flat table limit */ + entry_size = GITS_BASER_ENTRY_SIZE(baser->val); + if (!(baser->val & GITS_BASER_INDIRECT)) { + if (dev_id >= (PAGE_ORDER_TO_SIZE(baser->order) / entry_size)) + return false; + return true; + } + + /* Compute Level1 table index & check if that exceeds table range */ + idx = dev_id >> ilog2(baser->psz / entry_size); + if (idx >= (PAGE_ORDER_TO_SIZE(baser->order) / GITS_LVL1_ENTRY_SIZE)) + return false; + + table = baser->base; + + /* Allocate memory for Level2 table */ + if (!table[idx]) { + page = alloc_pages(GFP_KERNEL | __GFP_ZERO, get_order(baser->psz)); + if (!page) + return false; + + /* Flush memory to PoC if hardware doesn't support coherency */ + if (!(baser->val & GITS_BASER_SHAREABILITY_MASK)) + __flush_dcache_area(page_address(page), baser->psz); + + table[idx] = cpu_to_le64(page_to_phys(page) | GITS_BASER_VALID); + + /* Flush memory to PoC if hardware doesn't support coherency */ + if (!(baser->val & GITS_BASER_SHAREABILITY_MASK)) + __flush_dcache_area(table + idx, GITS_LVL1_ENTRY_SIZE); + + /* Ensure updated table contents are visible to ITS hardware */ + dsb(sy); + } + + return true; +} + static struct its_device *its_create_device(struct its_node *its, u32 dev_id, int nvecs) { - struct its_baser *baser; struct its_device *dev; unsigned long *lpi_map; unsigned long flags; @@ -1201,14 +1274,7 @@ static struct its_device *its_create_device(struct its_node *its, u32 dev_id, int nr_ites; int sz; - baser = its_get_baser(its, GITS_BASER_TYPE_DEVICE); - - /* Don't allow 'dev_id' that exceeds single, flat table limit */ - if (baser) { - if (dev_id >= (PAGE_ORDER_TO_SIZE(baser->order) / - GITS_BASER_ENTRY_SIZE(baser->val))) - return NULL; - } else if (ilog2(dev_id) >= its->device_ids) + if (!its_alloc_device_table(its, dev_id)) return NULL; dev = kzalloc(sizeof(*dev), GFP_KERNEL); -- Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
