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SubjectRe: [PATCH v2] irqchip/gic-v3: Ensure GICR_CTLR.EnableLPI=0 is observed before enabling
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Hi Marc,

On 03/17/2018 08:34 AM, Marc Zyngier wrote:
> On Thu, 15 Mar 2018 09:31:27 -0500
> Shanker Donthineni <shankerd@codeaurora.org> wrote:
>
>> The definition of the GICR_CTLR.RWP control bit was expanded to indicate
>> status of changing GICR_CTLR.EnableLPI from 1 to 0 is being in progress
>> or completed. Software must observe GICR_CTLR.RWP==0 after clearing
>> GICR_CTLR.EnableLPI from 1 to 0 and before writing GICR_PENDBASER and/or
>> GICR_PROPBASER, otherwise behavior is UNPREDICTABLE.
>>
>> Signed-off-by: Shanker Donthineni <shankerd@codeaurora.org>
>> ---
>> Changes since v1:
>> -Moved LPI disable code to a seperate function as Marc suggested.
>> -Mark's suggestion to use readl_relaxed_poll_timeout() helper functions.
>>
>> drivers/irqchip/irq-gic-v3-its.c | 66 ++++++++++++++++++++++++++++++--------
>> include/linux/irqchip/arm-gic-v3.h | 1 +
>> 2 files changed, 53 insertions(+), 14 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index 1d3056f..cba71a7 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -33,6 +33,8 @@
>> #include <linux/of_platform.h>
>> #include <linux/percpu.h>
>> #include <linux/slab.h>
>> +#include <linux/time64.h>
>> +#include <linux/iopoll.h>
>>
>> #include <linux/irqchip.h>
>> #include <linux/irqchip/arm-gic-v3.h>
>> @@ -1875,16 +1877,6 @@ static void its_cpu_init_lpis(void)
>> gic_data_rdist()->pend_page = pend_page;
>> }
>>
>> - /* Disable LPIs */
>> - val = readl_relaxed(rbase + GICR_CTLR);
>> - val &= ~GICR_CTLR_ENABLE_LPIS;
>> - writel_relaxed(val, rbase + GICR_CTLR);
>> -
>> - /*
>> - * Make sure any change to the table is observable by the GIC.
>> - */
>> - dsb(sy);
>> -
>> /* set PROPBASE */
>> val = (page_to_phys(gic_rdists->prop_page) |
>> GICR_PROPBASER_InnerShareable |
>> @@ -3288,13 +3280,59 @@ static bool gic_rdists_supports_plpis(void)
>> return !!(gic_read_typer(gic_data_rdist_rd_base() + GICR_TYPER) & GICR_TYPER_PLPIS);
>> }
>>
>> +static int redist_disable_lpis(void)
>> +{
>> + void __iomem *rbase = gic_data_rdist_rd_base();
>> + u64 val;
>> + int ret;
>> +
>> + if (!gic_rdists_supports_plpis()) {
>> + pr_info("CPU%d: LPIs not supported\n", smp_processor_id());
>> + return -ENXIO;
>> + }
>> +
>> + val = readl_relaxed(rbase + GICR_CTLR);
>> + if (!(val & GICR_CTLR_ENABLE_LPIS))
>> + return 0;
>> +
>> + /* Disable LPIs */
>> + val &= ~GICR_CTLR_ENABLE_LPIS;
>> + writel_relaxed(val, rbase + GICR_CTLR);
>> +
>> + /* Make sure any change to GICR_CTLR is observable by the GIC */
>> + dsb(sy);
>> +
>> + /* Wait for GICR_CTLR.GICR_CTLR_ENABLE_LPIS==0 or timeout */
>> + ret = readl_relaxed_poll_timeout_atomic(rbase + GICR_CTLR, val,
>> + !(val & GICR_CTLR_ENABLE_LPIS), 1,
>> + USEC_PER_SEC);
>
> Why do you need to poll on EnableLPIs? It is supposed to be immediately
> written. It seems to me that the sequence should be:
>

Agree we don't need to poll EnableLPIs here. I'll remove.

> - Check EnableLPis
> - If set to 1, scream about bootloader being braindead
> - Write EnableLPIs to 0
> - Read back EnableLpis:
> - If still set 1, bail out, we're doomed. Scream about the HW being
> braindead
> - Poll RWP
> - If timeout, bail out, the HW has locked up. Scream again.
>
> I think this should cover the whole thing. An alternative would be to
> place the poll between the write and read-back, but that doesn't change
> anything.
>

I'll prefer your second approach. Please comment on the below change before
I post v3.

static int redist_disable_lpis(void)
{
void __iomem *rbase = gic_data_rdist_rd_base();
u64 val;
int ret;

if (!gic_rdists_supports_plpis()) {
pr_info("CPU%d: LPIs not supported\n", smp_processor_id());
return -ENXIO;
}

if (!(readl(rbase + GICR_CTLR) & GICR_CTLR_ENABLE_LPIS))
return 0;

pr_warn("CPU%d: Trying to disable LPIs\n", smp_processor_id());
val &= ~GICR_CTLR_ENABLE_LPIS;
writel_relaxed(val, rbase + GICR_CTLR);

/* Make sure any change to GICR_CTLR is observable by the GIC */
dsb(sy);

/**
* Software must observe RWP==0 after clearing GICR_CTLR.EnableLPIs
* from 1 to 0 before programming GICR_PEND{PROP}BASER registers.
* Bail out the driver probe() in case of timeout.
*/
ret = readl_relaxed_poll_timeout_atomic(rbase + GICR_CTLR, val,
!(val & GICR_CTLR_RWP), 1,
USEC_PER_SEC);
if (ret) {
pr_err("CPU%d: EnableLPIs not observed\n", smp_processor_id());
return ret;
}

/**
* After it has been written to 1, it is IMPLEMENTATION DEFINED whether
* the bit GICR_CTLR.EnableLPI becomes RES1 or can be cleared to 0.
* Bail out the driver probe() on systems where it's RES1.
*/
if (readl_relaxed(rbase + GICR_CTLR) & GICR_CTLR_ENABLE_LPIS) {
pr_err("CPU%d: Failed to disable LPIs\n", smp_processor_id());
return -EPERM;
}

return 0;
}

>> + if (ret) {
>> + pr_err("CPU%d: Failed to disable LPIs\n", smp_processor_id());
>> + return -EBUSY;
>> + }
>> +
>> + /* Wait for GICR_CTLR.RWP==0 or timeout */
>> + ret = readl_relaxed_poll_timeout_atomic(rbase + GICR_CTLR, val,
>> + !(val & GICR_CTLR_RWP), 1,
>> + USEC_PER_SEC);
>> + if (ret) {
>> + pr_err("CPU%d: Failed to observe RWP==0 after enabling LPIs\n",
>> + smp_processor_id());
>> + return -EBUSY;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> int its_cpu_init(void)
>> {
>> + int ret;
>> +
>> if (!list_empty(&its_nodes)) {
>
> nit: move 'ret' here.
>
>> - if (!gic_rdists_supports_plpis()) {
>> - pr_info("CPU%d: LPIs not supported\n", smp_processor_id());
>> - return -ENXIO;
>> - }
>> + ret = redist_disable_lpis();
>> + if (ret)
>> + return ret;
>> +
>> its_cpu_init_lpis();
>> its_cpu_init_collection();
>> }
>> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
>> index c00c4c33..4d5fb60 100644
>> --- a/include/linux/irqchip/arm-gic-v3.h
>> +++ b/include/linux/irqchip/arm-gic-v3.h
>> @@ -106,6 +106,7 @@
>> #define GICR_PIDR2 GICD_PIDR2
>>
>> #define GICR_CTLR_ENABLE_LPIS (1UL << 0)
>> +#define GICR_CTLR_RWP (1UL << 3)
>>
>> #define GICR_TYPER_CPU_NUMBER(r) (((r) >> 8) & 0xffff)
>>
>
> 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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