Re: [PATCH v6 1/4] PCI: Introduce pci_dev_for_each_resource()

Bjorn Helgaas
2023-03-22T19:28:04Z

Hi Andy and Mika,

I really like the improvements here. They make the code read much
better.

On Mon, Mar 20, 2023 at 03:16:30PM +0200, Andy Shevchenko wrote:
> From: Mika Westerberg <mika.westerberg@linux.intel.com>
> ...

> static void fixup_winbond_82c105(struct pci_dev* dev)
> {
> - int i;
> + struct resource *r;
> unsigned int reg;
>
> if (!machine_is(pseries))
> @@ -251,14 +251,14 @@ static void fixup_winbond_82c105(struct pci_dev* dev)
> /* Enable LEGIRQ to use INTC instead of ISA interrupts */
> pci_write_config_dword(dev, 0x40, reg | (1<<11));
>
> - for (i = 0; i < DEVICE_COUNT_RESOURCE; ++i) {
> + pci_dev_for_each_resource_p(dev, r) {
> /* zap the 2nd function of the winbond chip */
> - if (dev->resource[i].flags & IORESOURCE_IO
> - && dev->bus->number == 0 && dev->devfn == 0x81)
> - dev->resource[i].flags &= ~IORESOURCE_IO;
> - if (dev->resource[i].start == 0 && dev->resource[i].end) {
> - dev->resource[i].flags = 0;
> - dev->resource[i].end = 0;
> + if (dev->bus->number == 0 && dev->devfn == 0x81 &&
> + r->flags & IORESOURCE_IO)

This is a nice literal conversion, but it's kind of lame to test
bus->number and devfn *inside* the loop here, since they can't change
inside the loop.

> + r->flags &= ~IORESOURCE_IO;
> + if (r->start == 0 && r->end) {
> + r->flags = 0;
> + r->end = 0;
> }
> }

> #define pci_resource_len(dev,bar) \
> ((pci_resource_end((dev), (bar)) == 0) ? 0 : \
> \
> - (pci_resource_end((dev), (bar)) - \
> - pci_resource_start((dev), (bar)) + 1))
> + resource_size(pci_resource_n((dev), (bar))))

I like this change, but it's unrelated to pci_dev_for_each_resource()
and unmentioned in the commit log.

> +#define __pci_dev_for_each_resource(dev, res, __i, vartype) \
> + for (vartype __i = 0; \
> + res = pci_resource_n(dev, __i), __i < PCI_NUM_RESOURCES; \
> + __i++)
> +
> +#define pci_dev_for_each_resource(dev, res, i) \
> + __pci_dev_for_each_resource(dev, res, i, )
> +
> +#define pci_dev_for_each_resource_p(dev, res) \
> + __pci_dev_for_each_resource(dev, res, __i, unsigned int)

This series converts many cases to drop the iterator variable ("i"),
which is fantastic.

Several of the remaining places need the iterator variable only to
call pci_claim_resource(), which could be converted to take a "struct
resource *" directly without much trouble.

We don't have to do that pci_claim_resource() conversion now, but
since we're converging on the "(dev, res)" style, I think we should
reverse the names so we have something like:

pci_dev_for_each_resource(dev, res)
pci_dev_for_each_resource_idx(dev, res, i)

Not sure __pci_dev_for_each_resource() is worthwhile since it only
avoids repeating that single "for" statement, and passing in "vartype"
(sometimes empty to implicitly avoid the declaration) is a little
complicated to read. I think it'd be easier to read like this:

#define pci_dev_for_each_resource(dev, res) \
for (unsigned int __i = 0; \
res = pci_resource_n(dev, __i), __i < PCI_NUM_RESOURCES; \
__i++)

#define pci_dev_for_each_resource_idx(dev, res, idx) \
for (idx = 0; \
res = pci_resource_n(dev, idx), idx < PCI_NUM_RESOURCES; \
idx++)

Bjorn