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

On Mon, Feb 1, 2016 at 7:18 PM, Yuanhan Liu [off-list ref] wrote:

On Fri, Jan 29, 2016 at 11:51:50PM +0530, Santosh Shukla wrote:

quoted

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 <redacted>
---
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

...

quoted

+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.

quoted

+
+     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?

quoted

+             return -1;
+     }
+}
+

...

quoted

+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