Re: [PATCH v2 2/3] IRQ/Gic-V3: Change arm-gic-its to support the Mbigen interrupt

["majun (F)" <majun258@huawei.com>]

在 2015/6/12 18:48, Thomas Gleixner 写道:
> On Fri, 12 Jun 2015, Ma Jun wrote:
> 
>> This patch is applied to support the mbigen interrupt.
>>
>> As a kind of MSI interrupt controller, the mbigen is used as a child 
>> domain of ITS domain just like PCI devices.
>> So the arm-gic-v3-its and related files are changed.
>>
>> The chip.c is also changed to check irq_ach before it called.
> 
> This patch wants to be split into several:
> 
> 1) Changes to the core code
> 
> 2) New functionality in the core code
> 
> 2) Changes to gic-v3-its
> 
> And all patches require proper changelogs which explain WHY these
> changes are necessary.
> 
> We can see which files are changed from the diffstat and the patch
> ourself. So no point to mention this in the changelog.
> 
> But we cannot figure out from looking at the code WHY you think that
> your approach to solve the problem is the right one.
> 
>>  void irq_chip_ack_parent(struct irq_data *data)
>>  {
>>  	data = data->parent_data;
>> -	data->chip->irq_ack(data);
>> +	if (data->chip->irq_ack)
>> +		data->chip->irq_ack(data);
> 
> Why is this required? Just because? Again, you fail to provide a
> rationale for the changes to the irq_chip*parent() functions.
> 
> Why would you call irq_chip_ack_parent() if that parent does not
> provide the required functionality in the first place?
> 

Yes, this is not a necessary callback. I will remove this callback
from mbigen driver.

>>  /*
>> @@ -363,6 +364,9 @@ struct irq_chip {
>>  	int		(*irq_request_resources)(struct irq_data *data);
>>  	void		(*irq_release_resources)(struct irq_data *data);
>>  
>> +	void		(*irq_compose_mbigen_msg)(struct irq_data *data, struct mbigen_msg *msg);
>> +	void		(*irq_write_mbigen_msg)(struct irq_data *data, struct mbigen_msg *msg);
>> +
> 
> What's so special about mbigen to justify extra callbacks which just
> bloat the data structure for everyone. Why are the msi callbacks not
> sufficient?
> 
> MBI is just another variant of MSI, right?
> 
yes,MBI is a kind of MSI which used for non-pci devices.

According to Marc's advice, the irq hierachy structure
in my patch likes below:
non-pci devices-->mbigen-->its-->gic
pci devices     -->msi __/

Eventhough the function *irq_compose_mbigen_msg does
the same thing as *irq_chip_compose_msi_msg, I still
added this function. Because I don't want mix the code
used by msi(pci devices) with the code used by mbigen.

> struct mbigen_msg {
>        u32     address_lo;
>        u32     address_hi;
>        u32     data;
> };
> 
> struct mbigen_msg is just a mindless copy of struct msi_msg:
> 
> struct msi_msg {
>         u32     address_lo;     /* low 32 bits of msi message address */
>         u32     address_hi;     /* high 32 bits of msi message address */
>         u32     data;           /* 16 bits of msi message data */
> };
> 
> So what's the point of this?
>

Based on the same reason, I also added  structure mbigen_msg for
mbigen using.

>>  	void		(*irq_compose_msi_msg)(struct irq_data *data, struct msi_msg *msg);
>>  	void		(*irq_write_msi_msg)(struct irq_data *data, struct msi_msg *msg);
>>  
> 
>> +
>> +/**
>> + * irq_chip_compose_mbigen_msg - Componse mbigen message for a mbigen irq chip
>> + * @data:	Pointer to interrupt specific data
>> + * @msg:	Pointer to the mbigen message
>> + *
>> + * For hierarchical domains we find the first chip in the hierarchy
>> + * which implements the irq_compose_mbigen_msg callback. For non
>> + * hierarchical we use the top level chip.
>> + */
>> +
>> +int irq_chip_compose_mbigen_msg(struct irq_data *data, struct mbigen_msg *msg)
>> +{
>> +	struct irq_data *pos = NULL;
>> +
>> +#ifdef	CONFIG_IRQ_DOMAIN_HIERARCHY
>> +	for (; data; data = data->parent_data)
>> +#endif
>> +		if (data->chip && data->chip->irq_compose_mbigen_msg)
>> +			pos = data;
>> +	if (!pos)
>> +		return -ENOSYS;
>> +
>> +	pos->chip->irq_compose_mbigen_msg(pos, msg);
>> +
>> +	return 0;
>> +}
> 
> Again, this is a completely useless copy of irq_chip_compose_msi_msg().
> Why can't you just use the existing callbacks and use struct msi_msg
> for your special chip?
> 
As mentioned before, to avoid using the code of msi, i added this
function.Because they are different domain.

If you don't mind, I can use the irq_chip_compose_msi_msg function in
mbigen driver instead of irq_chip_compose_mbigen_msg.

> And w/o looking at the mbigen code in detail, I bet it's nothing else
> than MSI for non PCI devices and contains tons of redundant and copied
> code, right?
>
> Can you please provide a proper description of this mbigen chip and
> explain WHY you think that it needs all this special hackery?
> 
> Thanks,
> 
> 	tglx
> 
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