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

Sanjay R Mehta
2021-06-16T12:01:07Z

On 6/16/2021 1:22 PM, Vinod Koul wrote:
> [CAUTION: External Email]
>
> 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)
>>>>>>>> +{
>>>>>>>> + 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 ?
>
> Trying to unroll further, who creates pt_device? who creates the dev
> object under this..?
>

Hi Vinod,

The pt_device is allocated and initialized in the PCI probe function and
then we just get the "dev" from the "pci_dev" object and save it in
"pt->dev" as shown in below snippet.

static int pt_pci_probe(struct pci_dev *pdev, const struct
pci_device_id *id)
{
struct pt_device *pt;
struct pt_msix *pt_msix;
struct device *dev = &pdev->dev;

Thanks,
- Sanjay