Re: [RFC 1/2] irqchip: irq-imx-gpcv2: Add workaround for i.MX8MQ ERR11171

[Marc Zyngier <marc.zyngier@arm.com>]

On 10/06/2019 15:12, Abel Vesa wrote:
> On 19-06-10 14:51:48, Marc Zyngier wrote:
>> On 10/06/2019 14:38, Abel Vesa wrote:
>>> On 19-06-10 14:24:11, Marc Zyngier wrote:
>>>> Abel,
>>>>
>>>> On 10/06/2019 13:13, Abel Vesa wrote:
>>>>> i.MX8MQ is missing the wake_request signals from GIC to GPCv2. This indirectly
>>>>> breaks cpuidle support due to inability to wake target cores on IPIs.
>>>>>
>>>>> Here is the link to the errata (see e11171):
>>>>>
>>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.nxp.com%2Fdocs%2Fen%2Ferrata%2FIMX8MDQLQ_0N14W.pdf&data=02%7C01%7Cabel.vesa%40nxp.com%7Cf74b196c8beb46599f8408d6edaace09%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C636957715230445874&sdata=ruP3qm1NTLTdoLC5XDu0uN5yNKLb4%2F2iP9kF5vdr1OI%3D&reserved=0
>>>>>
>>>>> Now, in order to fix this, we can trigger IRQ 32 (hwirq 0) to all the cores by
>>>>> setting 12th bit in IOMUX_GPR1 register. In order to control the target cores
>>>>> only, that is, not waking up all the cores every time, we can unmask/mask the
>>>>> IRQ 32 in the first GPC IMR register. So basically we can leave the IOMUX_GPR1
>>>>> 12th bit always set and just play with the masking and unmasking the IRO 32 for
>>>>> each independent core.
>>>>>
>>>>> Since EL3 is the one that deals with powering down/up the cores, and since the
>>>>> cores wake up in EL3, EL3 should be the one to control the IMRs in this case.
>>>>> This implies we need to get into EL3 on every IPI to do the unmasking, leaving
>>>>> the masking to be done on the power-up sequence by the core itself.
>>>>>
>>>>> In order to be able to get into EL3 on each IPI, we 'hijack' the registered smp
>>>>> cross call handler, in this case the gic_raise_softirq which is registered by
>>>>> the irq-gic-v3 driver and register our own handler instead. This new handler is
>>>>> basically a wrapper over the hijacked handler plus the call into EL3.
>>>>>
>>>>> To get into EL3, we use a custom vendor SIP id added just for this purpose.
>>>>>
>>>>> All of this is conditional for i.MX8MQ only.
>>>>>
>>>>> Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
>>>>> ---
>>>>>  drivers/irqchip/irq-imx-gpcv2.c | 42 +++++++++++++++++++++++++++++++++++++++++
>>>>>  1 file changed, 42 insertions(+)
>>>>>
>>>>> diff --git a/drivers/irqchip/irq-imx-gpcv2.c b/drivers/irqchip/irq-imx-gpcv2.c
>>>>> index 66501ea..b921105 100644
>>>>> --- a/drivers/irqchip/irq-imx-gpcv2.c
>>>>> +++ b/drivers/irqchip/irq-imx-gpcv2.c
>>>>> @@ -6,11 +6,19 @@
>>>>>   * published by the Free Software Foundation.
>>>>>   */
>>>>>  
>>>>> +#include <linux/arm-smccc.h>
>>>>> +#include <linux/mfd/syscon/imx6q-iomuxc-gpr.h>
>>>>> +#include <linux/mfd/syscon.h>
>>>>>  #include <linux/of_address.h>
>>>>>  #include <linux/of_irq.h>
>>>>> +#include <linux/regmap.h>
>>>>>  #include <linux/slab.h>
>>>>>  #include <linux/irqchip.h>
>>>>>  #include <linux/syscore_ops.h>
>>>>> +#include <linux/smp.h>
>>>>> +
>>>>> +#define IMX_SIP_GPC		0xC2000004
>>>>> +#define IMX_SIP_GPC_CORE_WAKE	0x00
>>>>>  
>>>>>  #define IMR_NUM			4
>>>>>  #define GPC_MAX_IRQS            (IMR_NUM * 32)
>>>>> @@ -73,6 +81,37 @@ static struct syscore_ops imx_gpcv2_syscore_ops = {
>>>>>  	.resume		= gpcv2_wakeup_source_restore,
>>>>>  };
>>>>>  
>>>>> +static void (*__gic_v3_smp_cross_call)(const struct cpumask *, unsigned int);
>>>>> +
>>>>> +static void imx_gpcv2_raise_softirq(const struct cpumask *mask,
>>>>> +					  unsigned int irq)
>>>>> +{
>>>>> +	struct arm_smccc_res res;
>>>>> +
>>>>> +	/* call the hijacked smp cross call handler */
>>>>> +	__gic_v3_smp_cross_call(mask, irq);
>>>>
>>>> I'm feeling a bit sick... :-(
>>>>
>>>>> +
>>>>> +	/* now call into EL3 and take care of the wakeup */
>>>>> +	arm_smccc_smc(IMX_SIP_GPC, IMX_SIP_GPC_CORE_WAKE,
>>>>> +			*cpumask_bits(mask), 0, 0, 0, 0, 0, &res);
>>>>
>>>> There is a number of things that look wrong here:
>>>>
>>>> - What guarantees that this SMC call actually exists? The DT itself just
>>>> says that this is broken, and not much about EL3.
>>>
>>> OK, that's easy to fix.
>>
>> Sure. How?
>>
> 
> If the SMC_UNK is returned, then we keep the IOMUX_GPR1 bit 12 set and the IMR1 bit 0
> for that core unset. That would always wake up the cores and therefore no the
> cpuidle will not have any effect.
> 
>>>
>>>>
>>>> - What guarantees that the cpumask matches the physical layout? I could
>>>> have booted via kexec, and logical CPU0 is now physical CPU3.
>>>>
>>>
>>> Fair point. I didn't think of that. Will have to put some thought into it.
>>>
>>>> - What if you have more than 64 CPUs? Probably not a big deal for this
>>>> particular instance, but I fully expect people to get it wrong again on
>>>> the next iteration if we "fix" it for them.
>>>
>>> That will never be the case. This is done in the irq-imx-gpcv2, so it
>>> won't be used by any other platform. It's just a workaround for the 
>>> gpcv2.
>>
>> "never"? That's a pretty strong statement. Given that the same IP has
>> been carried across a number of implementations, I fully expect imx9 (or
>> whatever the next generation is labeled) to use the same stuff.
>>
> 
> Again, this workaround will only apply to i.MX8MQ. IIRC, the gic500 was the
> one that added the wake_request signals, gic400 didn't gave them.
> And i.MX8MQ is the first NXP SoC to use the gic500. All the newer i.MX SoC
> which use GPCv2 don't have this issue. So it's obviously related to
> the switch from gic400 to gic500 when interfacing with GPCv2.

I can only admire your optimism.

> 
>>>
>>>>
>>>> - How does it work on a 32bit kernel, when firmware advertises a SMC64 call?
>>>>
>>>
>>> This is also easy to fix.
>>>
>>>> And also:
>>>>
>>>> - IMX_SIP_GMC doesn't strike me as a very distinctive name. It certainly
>>>> doesn't say *which* SiP is responsible for this wonderful thing. I
>>>> understand that they would like to stay anonymous, but still...
>>>>
>>>
>>> Fair point. The idea is to have a class of SIPs just for the GPC needed actions.
>>
>> I don't know what meaning you give to the "SIP" acronym, but the SMCCC
>> documentation clearly has a different definition:
>>
>> "SiP	: Silicon Partner. In this document, the silicon manufacturer."
>>
>> What I'm asking for is that the silicon vendor's name to be clearly
>> spoken out.
> 
> Fair point. TBH, I used the same naming I found in some other subsystems upstream.
> If you grep the tree for IMX_SIP you will find IMX_SIP_TIMER, IMX_SIP_SRTC and
> IMX_SIP_CPUFREQ.
> 
> So I only followed the pattern here.
> 
>>
>>> One thing that will come in the near future is the move of all the IMR 
>>> (Interrupt Mask Register) control (which is part of the GPC) to TF-A.
>>> This IMX_SIP_GPC will be extended then to every action required by the IMR
>>> and so on. Remember, GPC is more than a power controller. It's an irqchip
>>> too.
>>>
>>>> - It isn't clear what you gain from relying on the kernel to send the
>>>> SGI, while you could do the whole thing at EL3.
>>>
>>> OK, how would you suggest to wake a core on an IPI from EL3 ?
>>
>> Erm... By writing to the ICC_SGI1R_EL1 system register, directly from
>> EL3, just before you apply your workaround?
> 
> Right, but how will you know in EL3 that an IPI has been raised ?

Because that's what you do at EL3. Don't call into the GIC driver, but
just deal with IPIs entirely at EL3.

But that's a pretty moot point, as this workaround only addresses part
of the overall issue.

	M.
-- 
Jazz is not dead. It just smells funny...

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