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Date: Mon, 6 Jun 2016 13:59:52 +0100 From: Marc Zyngier <marc.zyngier@....com> To: Shanker Donthineni <shankerd@...eaurora.org>, linux-kernel <linux-kernel@...r.kernel.org>, linux-arm-kernel <linux-arm-kernel@...ts.infradead.org> Cc: Thomas Gleixner <tglx@...utronix.de>, Jason Cooper <jason@...edaemon.net>, Vikram Sethi <vikrams@...eaurora.org>, Philip Elcan <pelcan@...eaurora.org> Subject: Re: [PATCH V4 1/5] irqchip/gicv3-its: Introduce two helper functions for accessing BASERn On 06/06/16 06:40, Shanker Donthineni wrote: > This patch adds the two handy helper functions for reading and writing > ITS BASERn register. > > Signed-off-by: Shanker Donthineni <shankerd@...eaurora.org> > --- > drivers/irqchip/irq-gic-v3-its.c | 32 +++++++++++++++++++++++++------- > 1 file changed, 25 insertions(+), 7 deletions(-) > > diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c > index 5eb1f9e..6392c82 100644 > --- a/drivers/irqchip/irq-gic-v3-its.c > +++ b/drivers/irqchip/irq-gic-v3-its.c > @@ -56,13 +56,14 @@ struct its_collection { > }; > > /* > - * The ITS_BASER structure - contains memory information and cached > - * value of BASER register configuration. > + * The ITS_BASER structure - contains memory information, cached value > + * of BASER register configuration and register idx. > */ > struct its_baser { > void *base; > u64 val; > u32 order; > + u32 idx; > }; > > /* > @@ -824,6 +825,17 @@ static const char *its_base_type_string[] = { > [GITS_BASER_TYPE_RESERVED7] = "Reserved (7)", > }; > > +static u64 its_read_baser(struct its_node *its, struct its_baser *baser) > +{ > + return readq_relaxed(its->base + GITS_BASER + (baser->idx << 3)); > +} > + > +static void its_write_baser(struct its_node *its, struct its_baser *baser, > + u64 val) > +{ > + writeq_relaxed(val, its->base + GITS_BASER + (baser->idx << 3)); > +} > + > static void its_free_tables(struct its_node *its) > { > int i; > @@ -863,14 +875,20 @@ static int its_alloc_tables(const char *node_name, struct its_node *its) > its->device_ids = ids; > > for (i = 0; i < GITS_BASER_NR_REGS; i++) { > - u64 val = readq_relaxed(its->base + GITS_BASER + i * 8); > - u64 type = GITS_BASER_TYPE(val); > - u64 entry_size = GITS_BASER_ENTRY_SIZE(val); > + struct its_baser *baser = its->tables + i; > int order = get_order(psz); > + u64 val, type, entry_size; > int alloc_pages; > u64 tmp; > void *base; > > + /* Record the register index */ > + baser->idx = i; > + > + val = its_read_baser(its, baser); > + type = GITS_BASER_TYPE(val); > + entry_size = GITS_BASER_ENTRY_SIZE(val); > + > if (type == GITS_BASER_TYPE_NONE) > continue; > > @@ -939,8 +957,8 @@ retry_baser: > val |= alloc_pages - 1; > its->tables[i].val = val; > > - writeq_relaxed(val, its->base + GITS_BASER + i * 8); > - tmp = readq_relaxed(its->base + GITS_BASER + i * 8); > + its_write_baser(its, baser, val); > + tmp = its_read_baser(its, baser); > > if ((val ^ tmp) & GITS_BASER_SHAREABILITY_MASK) { > /* > Thanks to this abstraction, I now realize what I really hate about this idea of caching stuff in the its_baser structure: you end up with inconsistent data: - You store something in baser->val - You write something else using its_write_baser - You read something else using its_read_baser We have 3 sets of inconsistent data, and what they mean depends on the context. What I'm proposing is that its_write_baser always performs a read back, and stores that read in baser->val. This gives us a more consistent view of what's going on (the value we wanted, and what the HW is actually capable of). How about something like this, on top of my previous suggestion: diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c index 520d171..5591441 100644 --- a/drivers/irqchip/irq-gic-v3-its.c +++ b/drivers/irqchip/irq-gic-v3-its.c @@ -836,6 +836,7 @@ static void its_write_baser(struct its_node *its, struct its_baser *baser, { int idx = baser - its->tables; writeq_relaxed(val, its->base + GITS_BASER + (idx << 3)); + baser->val = its_read_baser(its, baser); } static int its_setup_baser(struct its_node *its, struct its_baser *baser, @@ -891,7 +892,7 @@ retry_baser: } its_write_baser(its, baser, val); - tmp = its_read_baser(its, baser); + tmp = baser->val; if ((val ^ tmp) & GITS_BASER_SHAREABILITY_MASK) { /* @@ -939,7 +940,6 @@ retry_baser: baser->order = order; baser->base = base; baser->psz = psz; - baser->val = val; tmp = indirect ? GITS_LVL1_ENTRY_SIZE : esz; pr_info("ITS@%pa: allocated %d %s @%lx (%s, esz %d, psz %dK, shr %d)\n", @@ -968,7 +968,7 @@ static bool its_parse_baser_device(struct its_node *its, struct its_baser *baser * table by reading bit at offset '62' after writing '1' to it. */ its_write_baser(its, baser, val | GITS_BASER_INDIRECT); - val = its_read_baser(its, baser); + val = baser->val; indirect = !!(val & GITS_BASER_INDIRECT); if (indirect) { Thanks, M. -- Jazz is not dead. It just smells funny...
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