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

[Amit Prakash Shukla <amitprakashs@marvell.com>]

Hi Thomas and Chengwen,

Thank you for the review and feedback. Please find my comment in-line.

Thanks,
Amit Shukla

> ----------------------------------------------------------------------
> Hi Thomas,
> 
> 
> 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.

> 
> 
> Thanks
> 
> 
> [1]
> https://urldefense.proofpoint.com/v2/url?u=https-
> 3A__patches.dpdk.org_project_dpdk_patch_20231208082835.2817601-
> 2D3-2Damitprakashs-
> 40marvell.com_&d=DwICaQ&c=nKjWec2b6R0mOyPaz7xtfQ&r=ALGdXl3fZgF
> GR69VnJLdSnADun7zLaXG1p5Rs7pXihE&m=b0t1Tduh89vXiJ7GQG0eb_yIMN
> k2aEkmL2losNL5qiqNycAqWUi7kLJRmmOunpvy&s=oy9mqDXsDKhXuVG9iy7
> SLmU_shlYhfjrglvjEoEQ4AM&e=
> 
> >
> >> + *
> >> + * @return
> >> + *   - rte_dma_dev structure pointer for the given device ID on success,
> NULL
> >> + *   otherwise.
> >> + */
> >> +__rte_internal
> >> +struct rte_dma_dev *rte_dma_pmd_get_dev_by_id(const int dev_id);
> > Again, const does not make sense here.
> >
> > Chengwen, please can you comment this patch as you maintain dmadev?
> >
> >