Re: [PATCH v9 1/3] dmaengine: ptdma: Initial driver for the AMD PTDMA

Greg KH
2021-06-16T07:59:36Z

On Wed, Jun 16, 2021 at 01:22:54PM +0530, Vinod Koul wrote:
> On 16-06-21, 12:27, Sanjay R Mehta wrote:
> >
> >
> > On 6/16/2021 11:46 AM, Greg KH wrote:
> > > [CAUTION: External Email]
> > >
> > > On Wed, Jun 16, 2021 at 10:24:52AM +0530, Sanjay R Mehta wrote:
> > >>
> > >>
> > >> On 6/16/2021 9:45 AM, Vinod Koul wrote:
> > >>> [CAUTION: External Email]
> > >>>
> > >>> On 15-06-21, 16:50, Sanjay R Mehta wrote:
> > >>>
> > >>>>>> +static struct pt_device *pt_alloc_struct(struct device *dev)

In looking at this, why are you dealing with a "raw" struct device?
Shouldn't this be a parent pointer? Why not pass in the real type that
this can be made a child of?

> > >>>>>> +{
> > >>>>>> + struct pt_device *pt;
> > >>>>>> +
> > >>>>>> + pt = devm_kzalloc(dev, sizeof(*pt), GFP_KERNEL);
> > >>>>>> +
> > >>>>>> + if (!pt)
> > >>>>>> + return NULL;
> > >>>>>> + pt->dev = dev;
> > >>>>>> + pt->ord = atomic_inc_return(&pt_ordinal);
> > >>>>>
> > >>>>> What is the use of this number?
> > >>>>>
> > >>>>
> > >>>> There are eight similar instances of this DMA engine on AMD SOC.
> > >>>> It is to differentiate each of these instances.
> > >>>
> > >>> Are they individual device objects?
> > >>>
> > >>
> > >> Yes, they are individual device objects.
> > >
> > > Then what is "ord" for? Why are you using an atomic variable for this?
> > > What does this field do? Why doesn't the normal way of naming a device
> > > come into play here instead?
> > >
> >
> > Hi Greg,
> >
> > The value of "ord" is incremented for each device instance and then it
> > is used to store different name for each device as shown in below snippet.
> >
> > pt->ord = atomic_inc_return(&pt_ordinal);
> > snprintf(pt->name, MAX_PT_NAME_LEN, "pt-%u", pt->ord);
>
> Okay why not use device->name ?

Ah, I missed this. Yes, do not have 2 names for the same structure,
that is wasteful and confusing.

thanks,

greg k-h