Re: [PATCH v1 2/2] arch/arm: time: Add support for parsing interrupts by names

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Michal,

> On 9 Mar 2023, at 11:05, Michal Orzel <michal.orzel@xxxxxxx> wrote:
> 
> 
> 
> On 09/03/2023 09:02, Bertrand Marquis wrote:
>> 
>> 
>> Hi Stefano,
>> 
>>> On 7 Mar 2023, at 22:02, Stefano Stabellini <sstabellini@xxxxxxxxxx> wrote:
>>> 
>>> On Tue, 7 Mar 2023, Bertrand Marquis wrote:
>>>>> On 7 Mar 2023, at 11:09, Andrei Cherechesu (OSS) 
>>>>> <andrei.cherechesu@xxxxxxxxxxx> wrote:
>>>>> 
>>>>> From: Andrei Cherechesu <andrei.cherechesu@xxxxxxx>
>>>>> 
>>>>> Added support for parsing the ARM generic timer interrupts DT
>>>>> node by the "interrupt-names" property, if it is available.
>>>>> 
>>>>> If not available, the usual parsing based on the expected
>>>>> IRQ order is performed.
>>>>> 
>>>>> Also added the "hyp-virt" PPI to the timer PPI list, even
>>>>> though it's currently not in use. If the "hyp-virt" PPI is
>>>>> not found, the hypervisor won't panic.
>>>>> 
>>>>> Signed-off-by: Andrei Cherechesu <andrei.cherechesu@xxxxxxx>
>>>>> ---
>>>>> xen/arch/arm/include/asm/time.h |  3 ++-
>>>>> xen/arch/arm/time.c             | 26 ++++++++++++++++++++++----
>>>>> 2 files changed, 24 insertions(+), 5 deletions(-)
>>>>> 
>>>>> diff --git a/xen/arch/arm/include/asm/time.h 
>>>>> b/xen/arch/arm/include/asm/time.h
>>>>> index 4b401c1110..49ad8c1a6d 100644
>>>>> --- a/xen/arch/arm/include/asm/time.h
>>>>> +++ b/xen/arch/arm/include/asm/time.h
>>>>> @@ -82,7 +82,8 @@ enum timer_ppi
>>>>>   TIMER_PHYS_NONSECURE_PPI = 1,
>>>>>   TIMER_VIRT_PPI = 2,
>>>>>   TIMER_HYP_PPI = 3,
>>>>> -    MAX_TIMER_PPI = 4,
>>>>> +    TIMER_HYP_VIRT_PPI = 4,
>>>>> +    MAX_TIMER_PPI = 5,
>>>>> };
>>>>> 
>>>>> /*
>>>>> diff --git a/xen/arch/arm/time.c b/xen/arch/arm/time.c
>>>>> index 433d7be909..794da646d6 100644
>>>>> --- a/xen/arch/arm/time.c
>>>>> +++ b/xen/arch/arm/time.c
>>>>> @@ -38,6 +38,14 @@ uint32_t __read_mostly timer_dt_clock_frequency;
>>>>> 
>>>>> static unsigned int timer_irq[MAX_TIMER_PPI];
>>>>> 
>>>>> +static const char *timer_irq_names[MAX_TIMER_PPI] = {
>>>>> +    [TIMER_PHYS_SECURE_PPI] = "sec-phys",
>>>>> +    [TIMER_PHYS_NONSECURE_PPI] = "phys",
>>>>> +    [TIMER_VIRT_PPI] = "virt",
>>>>> +    [TIMER_HYP_PPI] = "hyp-phys",
>>>>> +    [TIMER_HYP_VIRT_PPI] = "hyp-virt",
>>>>> +};
>>>>> +
>>>> 
>>>> I would need some reference or a pointer to some doc to check those.
>>>> 
>>>>> unsigned int timer_get_irq(enum timer_ppi ppi)
>>>>> {
>>>>>   ASSERT(ppi >= TIMER_PHYS_SECURE_PPI && ppi < MAX_TIMER_PPI);
>>>>> @@ -149,15 +157,25 @@ static void __init init_dt_xen_time(void)
>>>>> {
>>>>>   int res;
>>>>>   unsigned int i;
>>>>> +    bool has_names;
>>>>> +
>>>>> +    has_names = dt_property_read_bool(timer, "interrupt-names");
>>>>> 
>>>>>   /* Retrieve all IRQs for the timer */
>>>>>   for ( i = TIMER_PHYS_SECURE_PPI; i < MAX_TIMER_PPI; i++ )
>>>>>   {
>>>>> -        res = platform_get_irq(timer, i);
>>>>> -
>>>>> -        if ( res < 0 )
>>>>> +        if ( has_names )
>>>>> +            res = platform_get_irq_byname(timer, timer_irq_names[i]);
>>>>> +        else
>>>>> +            res = platform_get_irq(timer, i);
>>>>> +
>>>>> +        if ( res > 0 )
>>>> 
>>>> The behaviour of the code is changed here compared to the current
>>>> version as res = 0 will now generate a panic.
>>>> 
>>>> Some device tree might not specify an interrupt number and just put
>>>> 0 and Xen will now panic on those systems.
>>>> As I have no idea if such systems exists and the behaviour is modified
>>>> you should justify this and mention it in the commit message or keep
>>>> the old behaviour and let 0 go through without a panic.
>>>> 
>>>> @stefano, julien any idea here ? should just keep the old behaviour ?
>>> 
>>> platform_get_irq returns 0 if the irq is 0. The irq cannot be 0 because
>>> 0 is reserved for SGIs, not PPIs. So I think it is OK to consider 0 an
>>> error.
>> 
>> Problem here is that a DTB might not specify all interrupts and just put
>> 0 for the one not used (or not available for example if you have no secure
>> world).
> Xen requires presence of EL3,EL2 and on such system, at least the following 
> timers needs to be there
> according to Arm ARM:
> - EL3 phys (if EL3 is there)

This might be needed by EL3 but not by Xen.

> - EL1 phys (always)
> - EL1 virt (always)
> - NS EL2 phys (if EL2 is there)

Agree

> 
> therefore, if we get 0 for one of those, it means that something went wrong 
> and we shall consider
> it as an error.

Agree except for the EL3 one :-)

Cheers
Bertrand

> 
> ~Michal