Re: [PATCH v6 1/8] eal: pci: add api to rd/wr pci bar region

[Santosh Shukla <sshukla@mvista.com>]

On Mon, Feb 1, 2016 at 7:18 PM, Yuanhan Liu <yuanhan.liu@linux.intel.com> wrote:
> On Fri, Jan 29, 2016 at 11:51:50PM +0530, Santosh Shukla wrote:
>> Introducing below api for pci bar region rd/wr.
>> Api's are:
>> - rte_eal_pci_read_bar
>> - rte_eal_pci_write_bar
>>
>> Signed-off-by: Santosh Shukla <sshukla@mvista.com>
>> ---
>> v5-->v6:
>> - update api infor in rte_eal_version.map file
>>   suggested by david manchand.
>>
>>  lib/librte_eal/bsdapp/eal/eal_pci.c             |   19 ++++++++++++
>>  lib/librte_eal/bsdapp/eal/rte_eal_version.map   |    3 ++
>>  lib/librte_eal/common/include/rte_pci.h         |   38 +++++++++++++++++++++++
>>  lib/librte_eal/linuxapp/eal/eal_pci.c           |   34 ++++++++++++++++++++
>>  lib/librte_eal/linuxapp/eal/eal_pci_init.h      |    6 ++++
>>  lib/librte_eal/linuxapp/eal/eal_pci_vfio.c      |   28 +++++++++++++++++
>>  lib/librte_eal/linuxapp/eal/rte_eal_version.map |    3 ++
>>  7 files changed, 131 insertions(+)
>>
>> diff --git a/lib/librte_eal/bsdapp/eal/eal_pci.c b/lib/librte_eal/bsdapp/eal/eal_pci.c
>> index 95c32c1..2e535ea 100644
>> --- a/lib/librte_eal/bsdapp/eal/eal_pci.c
>> +++ b/lib/librte_eal/bsdapp/eal/eal_pci.c
> ...
>> +int rte_eal_pci_read_bar(const struct rte_pci_device *device,
>> +                      void *buf, size_t len, off_t offset,
>> +                      int bar_idx)
>> +
>> +{
>> +     const struct rte_intr_handle *intr_handle = &device->intr_handle;
>
> I'd suggest to reference this var inside pci_vfio_read/write_bar(), and
> pass device as the parmater instead.
>

(Sorry for late reply, I was travelling on Monday.)
Make sense.

>> +
>> +     switch (device->kdrv) {
>> +     case RTE_KDRV_VFIO:
>> +             return pci_vfio_read_bar(intr_handle, buf, len,
>> +                                      offset, bar_idx);
>> +     default:
>> +             RTE_LOG(ERR, EAL, "write bar not supported by driver\n");
>                                    ^^^^^
> typo.
>

Oh, r / write / read, right? sorry for typo error (:-

>
> BTW, I have a question about this API. Obviously, reading/writing bar
> space is supported with UIO (when memory resource is mmapped). And I
> know why you introduced such 2 APIs, for reading IO bar.
>
> So, here is the question: what are the 2 APIs for, for being gerneric
> APIs to read/write bar spaces, or just to read IO bar spaces? If it's
> former, the message is wrong; if it's later, you may better rename it
> to rte_eal_pci_read/write_io_bar()?
>

Current use-case is virtio: It is used as io_bar which is first
bar[1]. But implementation is generic, can be used to do rd/wr for
other bar index too. Also vfio facilitate user to do rd/wr to pci_bars
w/o mapping that bar, So apis will be useful for such cases in future.

AFAIU: uio has read/write_config api only and Yes if bar region mapped
then no need to do rd/wr, user can directly access the pci_memory. But
use-case of this api entirely different: unmapped memory by
application context i.e.. vfio_rd/wr-way {pread/pwrite-way}.

Is above explanation convincing? Pl. let me know.

[1] https://en.wikipedia.org/wiki/PCI_configuration_space (first bar
offset 0x010)

> David, what do you think of that?
>
>
>> +             return -1;
>> +     }
>> +}
>> +
> ...
>> +int
>> +pci_vfio_read_bar(const struct rte_intr_handle *intr_handle,
>> +               void *buf, size_t len, off_t offs, int bar_idx)
>> +{
>> +     if (bar_idx < VFIO_PCI_BAR0_REGION_INDEX
>> +        || bar_idx > VFIO_PCI_BAR5_REGION_INDEX) {
>
> A minor nit: it's more nature to put the '||' at the end of expression,
> instead of at the front:
>
>     if (bar_idx < VFIO_PCI_BAR0_REGION_INDEX ||
>         bar_idx > VFIO_PCI_BAR5_REGION_INDEX) {
>
>
>         --yliu