Re: [PATCH v4 7/9] x86, pci, ecam: mmconfig_64.c becomes default implementation for ECAM driver.

[Tomasz Nowicki]

On 11.03.2015 16:37, Rob Herring wrote:
> On Wed, Mar 11, 2015 at 9:12 AM, Tomasz Nowicki
> <tomasz.nowicki@xxxxxxxxxx> wrote:
> > Architectures which want to take advantage of ECAM generic goodness
>
> This is not necessarily an architecture decision. It is likely per host.
Right, good point.

> > should select CONFIG_PCI_ECAM_GENERIC. Otherwise, like x86 32bits machines,
> > are obligated to provide own low-level ECAM calls.
> >
> > Signed-off-by: Tomasz Nowicki <tomasz.nowicki@xxxxxxxxxx>
> > ---
>
> [...]
>
> > diff --git a/drivers/pci/ecam.c b/drivers/pci/ecam.c
> > index c588234..796b6e7 100644
> > --- a/drivers/pci/ecam.c
> > +++ b/drivers/pci/ecam.c
> > @@ -23,6 +23,119 @@ static DEFINE_MUTEX(pci_mmcfg_lock);
> >
> >   LIST_HEAD(pci_mmcfg_list);
> >
> > +#ifdef CONFIG_GENERIC_PCI_ECAM
> > +static char __iomem *pci_dev_base(unsigned int seg, unsigned int bus,
> > +                                 unsigned int devfn)
> > +{
> > +       struct pci_mmcfg_region *cfg = pci_mmconfig_lookup(seg, bus);
> > +
> > +       if (cfg && cfg->virt)
> > +               return cfg->virt + (PCI_MMCFG_BUS_OFFSET(bus) | (devfn << 12));
> > +       return NULL;
> > +}
> > +
> > +int pci_mmcfg_read(unsigned int seg, unsigned int bus,
> > +                         unsigned int devfn, int reg, int len, u32 *value)
> > +{
> > +       char __iomem *addr;
> > +
> > +       /* Why do we have this when nobody checks it. How about a BUG()!? -AK */
> > +       if (unlikely((bus > 255) || (devfn > 255) || (reg > 4095))) {
> > +err:           *value = -1;
> > +               return -EINVAL;
> > +       }
> > +
> > +       rcu_read_lock();
>
> What is the purpose of the rcu lock other than the old implementation had it?

Read/write calls consist on lookup RCU list (with MMCONFIG regions) and 
then corresponding operation. It is possible to hotplug another pci root 
bridge which leads to RCU list modification.

> > +       addr = pci_dev_base(seg, bus, devfn);
>
> The .map_bus op provides the same function if you restructure to use
> the generic accessors.

As you noticed, pci_mmcfg_{read,write} and 
pci_generic_config_{read,write} prototypes are different.

int pci_mmcfg_read(unsigned int seg, unsigned int bus,
                   unsigned int devfn, int reg, int len, u32 *value);
vs
int pci_generic_config_read(struct pci_bus *bus, unsigned int devfn,
                            int where, int size, u32 *val);

This is because pci_mmcfg_{read,write} can be used before pci root 
bridge initialization (while we have no struct pci_bus *bus) inside of 
ACPICA code (osl.c --> acpi_os_read_pci_configuration())

For that reason, I decide to create ECAM related new accessors which do 
not depend on host bridge presence. In other words, 
pci_generic_config_{read,write} can be built on pci_mmcfg_{read,write} 
but not the other way around.

In the light of above, I could not used .map_bus. I might not see a 
nicer way to solve that so any opinion/suggestion very appreciated :)

> > +       if (!addr) {
> > +               rcu_read_unlock();
> > +               goto err;
> > +       }
> > +
> > +       *value = pci_mmio_read(len, addr + reg);
> > +       rcu_read_unlock();
> > +
> > +       return 0;
> > +}
> > +
> > +int pci_mmcfg_write(unsigned int seg, unsigned int bus,
> > +                          unsigned int devfn, int reg, int len, u32 value)
> > +{
> > +       char __iomem *addr;
> > +
> > +       /* Why do we have this when nobody checks it. How about a BUG()!? -AK */
> > +       if (unlikely((bus > 255) || (devfn > 255) || (reg > 4095)))
> > +               return -EINVAL;
> > +
> > +       rcu_read_lock();
> > +       addr = pci_dev_base(seg, bus, devfn);
> > +       if (!addr) {
> > +               rcu_read_unlock();
> > +               return -EINVAL;
> > +       }
> > +
> > +       pci_mmio_write(len, addr + reg, value);
> > +       rcu_read_unlock();
> > +
> > +       return 0;
> > +}
> > +
> > +static void __iomem *mcfg_ioremap(struct pci_mmcfg_region *cfg)
> > +{
> > +       void __iomem *addr;
> > +       u64 start, size;
> > +       int num_buses;
> > +
> > +       start = cfg->address + PCI_MMCFG_BUS_OFFSET(cfg->start_bus);
> > +       num_buses = cfg->end_bus - cfg->start_bus + 1;
> > +       size = PCI_MMCFG_BUS_OFFSET(num_buses);
> > +       addr = ioremap_nocache(start, size);
> > +       if (addr)
> > +               addr -= PCI_MMCFG_BUS_OFFSET(cfg->start_bus);
> > +       return addr;
> > +}
> > +
> > +int __init pci_mmcfg_arch_init(void)
>
> Where would this be called for the case of the generic host and using DT?
I focused on sharing the code in ACPI context and did not consider DT. I 
think we can improve that code as next steps.

Tomasz
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