Re: [EXT] Re: [PATCH v2] lib/dmadev: get DMA device using device ID

[Thomas Monjalon <thomas@monjalon.net>]

09/02/2024 12:05, Amit Prakash Shukla:
> > On 2024/2/9 0:25, Thomas Monjalon wrote:
> > > 19/12/2023 12:00, Amit Prakash Shukla:
> > >> +struct rte_dma_dev *
> > >> +rte_dma_pmd_get_dev_by_id(const int dev_id)
> > > const does not make sense here for an int parameter.
> > 
> > 
> > I think it could be OK with const even if the parameter is not pointer.
> > 
> > However, most DPDK APIs do not have const for simple types (e.g.
> > int/uin16_t).
> > 
> > In this aspect, I think it's also OK to remove const of here for consistency.
> > 
> > 
> > >
> > >> +{
> > >> +	if (!rte_dma_is_valid(dev_id))
> > >> +		return NULL;
> > >> +
> > >> +	return &rte_dma_devices[dev_id];
> > >> +}
> > > [...]
> > >> +/**
> > >> + * @internal
> > >> + * Get the rte_dma_dev structure device pointer for the device id.
> > >> + *
> > >> + * @param dev_id
> > >> + *   Device ID value to select the device structure.
> > > This comment is not explanatory.
> > > What is an ID? Where does it come from?
> > > Where can we see such ID for DMA device?
> > 
> > This new API is used in the event-dma driver of cnxk [1]:
> > 
> > The rte_event_dma_adapter_vchan_add has parameter of dma_dev_id, and it
> > then
> > 
> > invoke (*dev->dev_ops->dma_adapter_vchan_add)(dev, dma_dev_id, vchan,
> > event),
> > 
> > at cnxk driver, this ops will check whether the DMA is
> > cnxk_dmadev_pci_driver.
> > 
> > I think this is because the cnxk's event-and-dma implement has deep coupling
> > 
> > (because the cnxk's event device could interact with another vendor's
> > dma device).
> > 
> > 
> > Maybe we should think of a better way to solve this kind of coupling
> > problem.
> 
> Id, is the DMA dev id which is used in looking up DMA dev. This API is in-line with the other libraries.
> Crypto library has an api rte_cryptodev_pmd_get_dev to get crypto device based on device id.

OK I think I understand.
It is the library ID, the same as returned by
int rte_dma_get_dev_id_by_name(const char *name);

I can remove the const and apply if you are OK.
I would just change this comment:

+ * @param dev_id
+ *   Device ID value to select the device structure.

into

+ *   DMA device index in dmadev library.