RFC for ideas to clean up PCI MSI code

RFC for ideas to clean up PCI MSI code

[Jiang Liu]

Hi Bjorn, Yijing and Thomas,
	Recently Yijing is trying to kill some weak functions in
drivers/pci/msi.c by using msi_chip mechanism. And it inspired me
that we could go one step further to kill those weak functions
at all and move common PCI MSI code into PCI core by using the
new hierarch irqdomain framework.
	The way to achieve the goal is:
1) arch code creates irqdomain for PCI MSI controllers. By default,
there's only one global PCI MSI irqdomain. But there's may be multiple
for some architecture like x86. So arch also need to implement a weak
function (I know you don't like weak functions):
	struct irq_domain *arch_get_pci_msi_irq_domain(struct pci_dev *);

2) replace
arch_setup_msi_irqs()/arch_setup_msi_irqs()/arch_teardown_msi_irqs()/arch_teardown_msi_irq()
with
irq_domain interfaces.

3) kill arch_msi_mask_irq()/arch_msi_mask_irq() by directly setting
irq_chip.irq_mask()/irq_unmask().

4) we could also find a way to kill arch_restore_msi_irqs() by using
new irqdomain interfaces.

For arch code to support the new MSI, it needs to implement callbacks in
msi_domain_ops and irq_chip. All other PCI MSI code becomes common
and will be moved into pci/msi.c. Proposed interfaces as below:

struct irq_chip {
        void            (*irq_compose_msi_msg)(struct irq_data *data,
struct msi_msg *msg);
};

struct msi_domain_ops {
        void (*calc_hwirq)(struct msi_domain_info *info, void *arg,
                           struct msi_desc *desc);
        irq_hw_number_t (*get_hwirq)(struct msi_domain_info *info, void
*arg);
        int (*msi_init)(struct irq_domain *domain, struct
msi_domain_info *info,
                        unsigned int virq, irq_hw_number_t hwirq, void
*arg);
        void (*msi_free)(struct irq_domain *domain,
                         struct msi_domain_info *info, unsigned int virq);
};

struct msi_domain_info {
        struct msi_domain_ops *ops;
        struct irq_chip *chip;
        void *data;
};

struct irq_domain *msi_create_irq_domain(struct device_node *of_node,
                                         struct msi_domain_info *info,
                                         struct irq_domain *parent);

So, what's your thoughts about the proposal? If now objection, I may
send out a draft version for x86 within about one week:)
Thanks!
Gerry

Re: RFC for ideas to clean up PCI MSI code

[Yijing Wang]

On 2014/11/12 1:53, Jiang Liu wrote:
> Hi Bjorn, Yijing and Thomas,
> 	Recently Yijing is trying to kill some weak functions in
> drivers/pci/msi.c by using msi_chip mechanism. And it inspired me
> that we could go one step further to kill those weak functions
> at all and move common PCI MSI code into PCI core by using the
> new hierarch irqdomain framework.
> 	The way to achieve the goal is:
> 1) arch code creates irqdomain for PCI MSI controllers. By default,
> there's only one global PCI MSI irqdomain. But there's may be multiple
> for some architecture like x86. So arch also need to implement a weak
> function (I know you don't like weak functions):
> 	struct irq_domain *arch_get_pci_msi_irq_domain(struct pci_dev *);

Arm also may have multiple msi_chips/msi irq domains, currently, corresponding msi_chip is stored
in bus->msi. But it's not a good idea, I'm refactoring generic pci host bridge, we could
save it in generic pci_host_bridge.

> 
> 2) replace
> arch_setup_msi_irqs()/arch_setup_msi_irqs()/arch_teardown_msi_irqs()/arch_teardown_msi_irq()
> with
> irq_domain interfaces.

Agree.

> 
> 3) kill arch_msi_mask_irq()/arch_msi_mask_irq() by directly setting
> irq_chip.irq_mask()/irq_unmask().

arch_msi_mask_irq() is only called in pci_msi_shutdown, in this case,
the msi mask status will not be overrode, so we can restore it later.
If use irq_chip.irq_mask(), we need another place to save the mask status.

> 
> 4) we could also find a way to kill arch_restore_msi_irqs() by using
> new irqdomain interfaces.

My personal opinion, I think place arch_retore_msi_irqs() stuffs in irq_chip is better. :)


> 
> For arch code to support the new MSI, it needs to implement callbacks in
> msi_domain_ops and irq_chip. All other PCI MSI code becomes common
> and will be moved into pci/msi.c. Proposed interfaces as below:
> 
> struct irq_chip {
>         void            (*irq_compose_msi_msg)(struct irq_data *data,
> struct msi_msg *msg);
> };
> 
> struct msi_domain_ops {
>         void (*calc_hwirq)(struct msi_domain_info *info, void *arg,
>                            struct msi_desc *desc);
>         irq_hw_number_t (*get_hwirq)(struct msi_domain_info *info, void
> *arg);
>         int (*msi_init)(struct irq_domain *domain, struct
> msi_domain_info *info,
>                         unsigned int virq, irq_hw_number_t hwirq, void
> *arg);
>         void (*msi_free)(struct irq_domain *domain,
>                          struct msi_domain_info *info, unsigned int virq);
> };
> 
> struct msi_domain_info {
>         struct msi_domain_ops *ops;
>         struct irq_chip *chip;
>         void *data;
> };
> 
> struct irq_domain *msi_create_irq_domain(struct device_node *of_node,
>                                          struct msi_domain_info *info,
>                                          struct irq_domain *parent);
> 
> So, what's your thoughts about the proposal? If now objection, I may
> send out a draft version for x86 within about one week:)

I think the proposal is better than original msi_chip framework.
I like this idea. :)

Thanks!
Yijing.


> Thanks!
> Gerry
> 
> .
> 


-- 
Thanks!
Yijing