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

Sanjay R Mehta
2021-06-16T06:57:48Z

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)
>>>>>> +{
>>>>>> + 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);

- Sanjay