Re: [RFC v3 5/7] dmaengine: Add Synopsys eDMA IP PCIe glue-logic

[Gustavo Pimentel <gustavo.pimentel@synopsys.com>]

On 15/01/2019 05:43, Andy Shevchenko wrote:
> On Mon, Jan 14, 2019 at 11:38:02AM +0000, Gustavo Pimentel wrote:
>> On 11/01/2019 19:47, Andy Shevchenko wrote:
>>> On Fri, Jan 11, 2019 at 07:33:41PM +0100, Gustavo Pimentel wrote:
> 
>>>> +static bool disable_msix;
>>>> +module_param(disable_msix, bool, 0644);
>>>> +MODULE_PARM_DESC(disable_msix, "Disable MSI-X interrupts");
>>>
>>> Why?!
>>> We are no allow new module parameters without very strong arguments.
>>
>> Since this is a reference driver and might be used to test customized HW
>> solutions, I added this parameter to allow the possibility to test the solution
>> forcing the MSI feature binding. This is required specially if who will test
>> this solution has a Root Complex with both features available (MSI and MSI-X),
>> because the Kernel will give always preference to MSI-X binding (assuming that
>> the EP has also both features available).
> 
> Yes, you may do it for testing purposes, but it doesn't fit the kernel standards.

Ok, but how should I proceed? May I leave it or substitute by another way to do
it? If so, how?
As I said, the intended is to be only used for this test case, on normal
operation the parameter it should be always false.

> 
>>>> +	if (!pdata) {
>>>> +		dev_err(dev, "%s missing data structure\n", pci_name(pdev));
>>>> +		return -EFAULT;
>>>> +	}
>>>
>>> Useless check.
>>
>> Why? It's just a precaution, isn't it a good practice always to think of the
>> worst case?
> 
> You just can put an implicit requirement of pdata rather than doing this

Ok, how can I do it? What I should add to the code to force that?

> useless check. I don't believe it would make sense to have NULL pdata for the
> driver since it wouldn't be functional anyhow.

Yes, you're right without pdata the driver can't do anything.
> 
>>>> +	/* Mapping PCI BAR regions */
>>>> +	err = pcim_iomap_regions(pdev, BIT(pdata->rg_bar) |
>>>> +				       BIT(pdata->ll_bar) |
>>>> +				       BIT(pdata->dt_bar),
>>>> +				 pci_name(pdev));
>>>> +	if (err) {
> 
>>>> +		return err;
>>>> +	}
> 
>>>> +	if (!pcim_iomap_table(pdev))
>>>> +		return -EACCES;
>>>
>>> Never happen condition. Thus useless.
>>
>> pcim_iomap_table() can return NULL in case of allocation failure. Besides that,
>> isn't it a good practice always to think of the worst case?
> 
> No, it can't in the conditions your have in the code. See above the lines I left.
> If pcim_iomap_regions() successfully finished...

Nice catch, I didn't saw that. I added that validation because of coverity
analysis. I'll add a comment here to suppress this coverity false positive error.

> 
>>>> +	dev_info(dev, "DesignWare eDMA PCIe driver loaded completely\n");
>>>
>>> Useless.
>>
>> It's helpful for bring up, I can pass it to dbg.
> 
> It just shows that someone didn't use existing tools and features. This message and similar are useless.
> Hint: initcall_debug.

I wasn't aware of it. Thanks for the hint :)

> 
>>>> +	dev_info(dev, "DesignWare eDMA PCIe driver unloaded completely\n");
>>>
>>> Ditto.
>>
>> It's helpful for bring up, I can pass it to dbg.
> 
> Ditto.
>