On 2017-01-19 08:48, Phil Reid wrote:
> On 18/01/2017 20:19, Peter Rosin wrote:
>> On 2017-01-17 09:00, Phil Reid wrote:
>>> Unfortunately some hardware device will assert their irq line immediately
>>> on power on and provide no mechanism to mask the irq. As the i2c muxes
>>> provide no method to mask irq line this provides a work around by keeping
>>> the parent irq masked until enough device drivers have loaded to service
>>> all pending interrupts.
>>>
>>> For example the the ltc1760 assert its SMBALERT irq immediately on power
>>> on. With two ltc1760 attached to bus 0 & 1 on a pca954x mux when the first
>>> device is registered irq are enabled and fire continuously as the second
>>> device driver has not yet loaded. Setting this parameter to <1 1> will
>>> delay the irq being enabled until both devices are ready.
>>>
>>> Signed-off-by: Phil Reid <preid@xxxxxxxxxxxxxxxxx>
>>> ---
>>> drivers/i2c/muxes/i2c-mux-pca954x.c | 33 ++++++++++++++++++++++++++++++---
>>> 1 file changed, 30 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c b/drivers/i2c/muxes/i2c-mux-pca954x.c
>>> index f55da88..012b2ef 100644
>>> --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
>>> +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
>>> @@ -76,6 +76,19 @@ struct chip_desc {
>>> } muxtype;
>>> };
>>>
>>> +/*
>>> + * irq_mask_enable: Provides a mechanism to work around hardware that asserts
>>> + * their irq immediately on power on. It allows the enabling of the irq to be
>>> + * delayed until the corresponding bits in the the irq_mask are set thru
>>> + * irq_unmask.
>>> + * For example the ltc1760 assert its SMBALERT irq immediately on power on.
>>> + * With two ltc1760 attached to bus 0 & 1 on a pca954x mux when the first
>>> + * device is registered irq are enabled and fire continuously as the second
>>> + * device driver has not yet loaded. Setting this parameter to 0x3 while
>>> + * delay the irq being enabled until both devices are ready.
>>> + * This workaround will not work if two devices share an interrupt on the
>>> + * same bus segment.
>>
>> It will also not work if something shares the interrupt with the pca954x mux,
>> on the parent side of the mux, so to speak. Then that other driver may
>> potentially enable the irq "behind the back" of the pca954x driver.
>>
>>> + */
>>> struct pca954x {
>>> const struct chip_desc *chip;
>>>
>>> @@ -84,7 +97,9 @@ struct pca954x {
>>> struct i2c_client *client;
>>>
>>> struct irq_domain *irq;
>>> + unsigned int irq_mask_enable;
>>> unsigned int irq_mask;
>>> + bool irq_enabled;
>>> spinlock_t lock;
>>> };
>>>
>>> @@ -266,8 +281,10 @@ static void pca954x_irq_mask(struct irq_data *idata)
>>> spin_lock_irqsave(&data->lock, flags);
>>>
>>> data->irq_mask &= ~BIT(pos);
>>> - if (!data->irq_mask)
>>> + if (data->irq_enabled && !data->irq_mask) {
>>> disable_irq(data->client->irq);
>>> + data->irq_enabled = false;
>>> + }
>>
>> When irq_mask_enable is non-zero, I think the parent irq should be masked
>> when the first irq from the set in irq_mask_enable is masked. For symmetry.
>>
>> Like so (untested):
>>
>> if (data->irq_enabled) {
>> if (!data->irq_mask ||
>> (data->irq_mask & mask_enable) != mask_enable) {
>> disable_irq(data->client->irq);
>> data->irq_enabled = false;
>> }
>> }
> Yeap this make sense.
>
>>
>> Hmm, this whole thing is fiddly and while it solves your problem it doesn't
>> allow for solving the more general problem when there are "problematic"
>> devices mixed with other devices. At least, I don't see it. And the
>> limitations we are walking into with tracking number of enables etc suggests
>> that we are attacking this at the wrong level. Maybe you should try to work
>> around the hw limitations not in the pca954x driver, but in the irq core?
>
> I'm looking at the option of getting the hardware changed to not route
> the irq for my chips thru the i2c mux. Fortunately the hardware is going thru a
> revision for some other changes. Messing with the irq core sounds dangerous
> with my level of knowledge.
Yeah, but I bet you'd get some attention from people with more irq
experience. That can't be bad :-)
> The other way I think I can tackle it after reading the datasheet for the ltc1760 is that
> it'll deassert it's irq (smbalert) line when the host sends a ARA request on the bus segment.
> There's a driver in the kernel for this already, but it's not DT enable and doesn't
> handle multiple bus segments. I'll have a look at that as well.
> Pretty sure it would need the mux to become an irq parent as per patch 1-3 of this series.
> This would be so the system can figure out which segment to do the poll on.
Yeah sounds neater. It has the slight drawback that it may not work
for pure i2c buses since it an SMB thing??
BTW, why do you need special treatment for multiple segments? Will it not
simply have an ARA appear on whatever i2c bus the device sits on? And if
something requests to send an ARA message on a bus that happens to be a
muxed segment, my mental picture is that the mux will be operated as usual
so that the ARA appears on the muxed segment. Maybe I'm missing something?
> But p4-5 could be dropped which is where we're stuck I think.
Yes, I dislike to add a workaround for a specific case that might get
in the way for anybody wishing to fix a bigger, more generic, problem...
> Looking at this approach it shouldn't matter if the ltc1760 driver has registered yet or not.
> This approach possibly has a lot more generic appeal I think.
>
> Thoughts on just submitting p1-3 for now while I figure out the SMB alert approach?
Yes, looks like a plan. Thanks in advance!
>> I.e. have the irq core check, for each irq, for a property that specifies
>> the depth at which each irq should be unmasked. This new property should
>> probably be located in the interrupt-controller node? Then the code can
>> unmask interrupts when the depth hits this mark, instead of always unmasking
>> the interrupt when the depth changes from zero to one. You are then adding
>> the workaround at a level where there is enough information to fix the
>> more general problem. I think?
>>
>> But, once again, I'm no irq expert and would desperately like a second
>> opinion on this stuff...
>>
>>>
>>> spin_unlock_irqrestore(&data->lock, flags);
>>> }
>>> @@ -275,14 +292,18 @@ static void pca954x_irq_mask(struct irq_data *idata)
>>> static void pca954x_irq_unmask(struct irq_data *idata)
>>> {
>>> struct pca954x *data = irq_data_get_irq_chip_data(idata);
>>> + unsigned int mask_enable = data->irq_mask_enable;
>>> unsigned int pos = idata->hwirq;
>>> unsigned long flags;
>>>
>>> spin_lock_irqsave(&data->lock, flags);
>>>
>>> - if (!data->irq_mask)
>>> - enable_irq(data->client->irq);
>>> data->irq_mask |= BIT(pos);
>>> + if (!data->irq_enabled
>>> + && (data->irq_mask & mask_enable) == mask_enable) {
>>
>> I think the coding standard says that the && should be at the end of the
>> first line. Didn't checkpatch complain?
>
> No it didn't complain. and I wasn't sure which way to do this.
Ah, you need the --strict option for that to show up...
Cheers,
peda
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