Re: [Qemu-devel] [PATCH v2 1/6] msix: Add simple BAR allocation MSIX setup functions

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-06-14 17:49, Michael S. Tsirkin wrote:
> On Wed, Jun 13, 2012 at 10:51:19PM -0600, Alex Williamson wrote:
>> msi_init() takes over a BAR without really specifying or allowing
>> specification of how it does so.  Instead, let's split it into
>> two interfaces, one fully specified, and one trivially easy.  This
>> implements the latter.  msix_init_exclusive_bar() takes over
>> allocating and filling a PCI BAR _exclusively_ for the use of MSIX.
>> When used, the matching msi_uninit_exclusive_bar() should be used
>> to tear it down.
>>
>> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
>> ---
>>
>>  hw/msix.c |   43 +++++++++++++++++++++++++++++++++++++++++++
>>  hw/msix.h |    3 +++
>>  hw/pci.h  |    2 ++
>>  3 files changed, 48 insertions(+)
>>
>> diff --git a/hw/msix.c b/hw/msix.c
>> index b64f109..a4cdfb0 100644
>> --- a/hw/msix.c
>> +++ b/hw/msix.c
>> @@ -299,6 +299,41 @@ err_config:
>>      return ret;
>>  }
>>  
>> +int msix_init_exclusive_bar(PCIDevice *dev, unsigned short nentries,
>> +                            uint8_t bar_nr)
>> +{
>> +    int ret;
>> +    char *name;
>> +
>> +    /*
>> +     * Migration compatibility dictates that this remains a 4k
>> +     * BAR with the vector table in the lower half and PBA in
>> +     * the upper half.
>> +     */
>> +    if (nentries * PCI_MSIX_ENTRY_SIZE > 2048) {
>> +        return -EINVAL;
>> +    }
>> +
>> +    if (asprintf(&name, "%s MSIX BAR", dev->name) == -1) {
>> +        return -ENOMEM;
>> +    }
>> +
>> +    memory_region_init(&dev->msix_exclusive_bar, name, 4096);
>> +
>> +    free(name);
>> +
>> +    ret = msix_init(dev, nentries, &dev->msix_exclusive_bar, bar_nr, 4096);
>> +    if (ret) {
>> +        memory_region_destroy(&dev->msix_exclusive_bar);
>> +        return ret;
>> +    }
>> +
>> +    pci_register_bar(dev, bar_nr, PCI_BASE_ADDRESS_SPACE_MEMORY,
>> +                     &dev->msix_exclusive_bar);
>> +
>> +    return 0;
>> +}
>> +
>>  static void msix_free_irq_entries(PCIDevice *dev)
>>  {
>>      int vector;
>> @@ -329,6 +364,14 @@ int msix_uninit(PCIDevice *dev, MemoryRegion *bar)
>>      return 0;
>>  }
>>  
>> +void msix_uninit_exclusive_bar(PCIDevice *dev)
>> +{
>> +    if (msix_present(dev)) {
>> +        msix_uninit(dev, &dev->msix_exclusive_bar);
>> +        memory_region_destroy(&dev->msix_exclusive_bar);
>> +    }
>> +}
>> +
>>  void msix_save(PCIDevice *dev, QEMUFile *f)
>>  {
>>      unsigned n = dev->msix_entries_nr;
>> diff --git a/hw/msix.h b/hw/msix.h
>> index e5a488d..bed6bfb 100644
>> --- a/hw/msix.h
>> +++ b/hw/msix.h
>> @@ -7,11 +7,14 @@
>>  int msix_init(PCIDevice *pdev, unsigned short nentries,
>>                MemoryRegion *bar,
>>                unsigned bar_nr, unsigned bar_size);
>> +int msix_init_exclusive_bar(PCIDevice *dev, unsigned short nentries,
>> +                            uint8_t bar_nr);
>>  
>>  void msix_write_config(PCIDevice *pci_dev, uint32_t address,
>>                         uint32_t val, int len);
>>  
>>  int msix_uninit(PCIDevice *d, MemoryRegion *bar);
>> +void msix_uninit_exclusive_bar(PCIDevice *dev);
>>  
>>  unsigned int msix_nr_vectors_allocated(const PCIDevice *dev);
>>  
>> diff --git a/hw/pci.h b/hw/pci.h
>> index 4c96268..d517a54 100644
>> --- a/hw/pci.h
>> +++ b/hw/pci.h
>> @@ -226,6 +226,8 @@ struct PCIDevice {
>>  
>>      /* Space to store MSIX table */
>>      uint8_t *msix_table_page;
>> +    /* MemoryRegion container for msix exclusive BAR setup */
>> +    MemoryRegion msix_exclusive_bar;
> 
> Wrappers are good but this doesn't belong in PCIDevice IMO.
> E.g. when I debug and look at data structure I don't want to dig into
> code and go "oh this device uses an exclusive bar to it's here, that one
> uses a non exlcusive so the field is invalid, the real bar is over
> there.
> 
> Keep the region in devices where it was, pass to msix_init_exclusive_bar
> by parameter.

I disagree. There are plenty of fields in PCIDevice that are only used
under certain circumstances. This is just +1, and it makes the interface
usage much easier.

Jan

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