[dpdk-dev] [PATCH v3] dmadev: introduce DMA device library

Bruce Richardson bruce.richardson at intel.com
Thu Jul 15 11:03:05 CEST 2021


On Thu, Jul 15, 2021 at 12:40:01PM +0530, Jerin Jacob wrote:
> )
>  a
> 
> On Tue, Jul 13, 2021 at 6:01 PM Chengwen Feng <fengchengwen at huawei.com> wrote:
> >
> > This patch introduce 'dmadevice' which is a generic type of DMA
> > device.
> >
> > The APIs of dmadev library exposes some generic operations which can
> > enable configuration and I/O with the DMA devices.
> >
> > Signed-off-by: Chengwen Feng <fengchengwen at huawei.com>
> 
> Thanks for v3. Seems like all major items as covered. Some more
> comments below inline.
> 
> I would suggest v4 to split the patch like (so that we can review and
> ack each patch)
> 1) Only public header file with Doxygen inclusion, (There is a lot of
> Doxygen syntax issue in the patch)
> 2) 1 or more patches for implementation.
> 

One additional follow-up comment on flags below.

/Bruce

> 
> > diff --git a/lib/dmadev/rte_dmadev.h b/lib/dmadev/rte_dmadev.h
> > new file mode 100644
> > index 0000000..f6cc4e5
<snip>
> > +       enum rte_dmadev_port_type port_type;
> missing doxgen comment for this.
> > +       union {
> > +               /** For PCIE port
> > +                *
> > +                * The following model show SoC's PCIE module connects to
> > +                * multiple PCIE hosts and multiple endpoints. The PCIE module
> > +                * has an integrate DMA controller.
> > +                * If the DMA wants to access the memory of host A, it can be
> > +                * initiated by PF1 in core0, or by VF0 of PF0 in core0.
> > +                *
<snip>
> +                       /** The pasid filed in TLP packet */
> > +                       uint64_t pasid : 20;
> > +                       /** The attributes filed in TLP packet */
> > +                       uint64_t attr : 3;
> > +                       /** The processing hint filed in TLP packet */
> > +                       uint64_t ph : 2;
> > +                       /** The steering tag filed in TLP packet */
> > +                       uint64_t st : 16;
> 
> We don't support a few attributes like passid, ph, st. Do we need
> the capability of this? or ignore this. In either case, please update the doc.
> 
> We also support additional flags for allocating LLC flag.
> This is a hint to DMA engine that the cache blocks should be allocated
> in the LLC (if they were not already).
> When the MEM pointer is a destination in DMA operation, the referenced
> cache blocks are allocated into the cache as part of completing the
> DMA (when not already present in the LLC)
> this is helpful if software has to access the data right after dma is completed.
> 
> Could you add bit or flag for the same?
> 

I wonder if this is the best location for such a flag for LLC vs memory
writes. It would also apply to memory-to-memory transactions, not just for
those done to PCI devices. As well as that, I think any flag should default
to "on" rather than "off" since writing to cache rather than DRAM is
generally the desired behaviour, I would think. Should it be a
per-operation flag, rather than per context?

<snip>


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