Re: [PATCH v3 1/2] PCI: dwc: Add dbi_phys_addr and atu_phys_addr to struct dw_pcie

[Prudhvi Yarlagadda]

On 8/2/2024 2:22 AM, Serge Semin wrote:
> On Fri, Aug 02, 2024 at 10:52:06AM +0530, Manivannan Sadhasivam wrote:
>> On Fri, Aug 02, 2024 at 12:59:57AM +0300, Serge Semin wrote:
>>> On Thu, Aug 01, 2024 at 02:29:49PM -0700, Prudhvi Yarlagadda wrote:
>>>> Hi Serge,
>>>>
>>>> Thanks for the review comment.
>>>>
>>>> On 8/1/2024 12:25 PM, Serge Semin wrote:
>>>>> On Tue, Jul 23, 2024 at 07:27:18PM -0700, Prudhvi Yarlagadda wrote:
>>>>>> Both DBI and ATU physical base addresses are needed by pcie_qcom.c
>>>>>> driver to program the location of DBI and ATU blocks in Qualcomm
>>>>>> PCIe Controller specific PARF hardware block.
>>>>>>
>>>>>> Signed-off-by: Prudhvi Yarlagadda <quic_pyarlaga@xxxxxxxxxxx>
>>>>>> Reviewed-by: Mayank Rana <quic_mrana@xxxxxxxxxxx>
>>>>>> ---
>>>>>>  drivers/pci/controller/dwc/pcie-designware.c | 2 ++
>>>>>>  drivers/pci/controller/dwc/pcie-designware.h | 2 ++
>>>>>>  2 files changed, 4 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/pci/controller/dwc/pcie-designware.c b/drivers/pci/controller/dwc/pcie-designware.c
>>>>>> index 1b5aba1f0c92..bc3a5d6b0177 100644
>>>>>> --- a/drivers/pci/controller/dwc/pcie-designware.c
>>>>>> +++ b/drivers/pci/controller/dwc/pcie-designware.c
>>>>>> @@ -112,6 +112,7 @@ int dw_pcie_get_resources(struct dw_pcie *pci)
>>>>>>  		pci->dbi_base = devm_pci_remap_cfg_resource(pci->dev, res);
>>>>>>  		if (IS_ERR(pci->dbi_base))
>>>>>>  			return PTR_ERR(pci->dbi_base);
>>>>>> +		pci->dbi_phys_addr = res->start;
>>>>>>  	}
>>>>>>  
>>>>>>  	/* DBI2 is mainly useful for the endpoint controller */
>>>>>> @@ -134,6 +135,7 @@ int dw_pcie_get_resources(struct dw_pcie *pci)
>>>>>>  			pci->atu_base = devm_ioremap_resource(pci->dev, res);
>>>>>>  			if (IS_ERR(pci->atu_base))
>>>>>>  				return PTR_ERR(pci->atu_base);
>>>>>> +			pci->atu_phys_addr = res->start;
>>>>>>  		} else {
>>>>>>  			pci->atu_base = pci->dbi_base + DEFAULT_DBI_ATU_OFFSET;
>>>>>>  		}
>>>>>> diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
>>>>>> index 53c4c8f399c8..efc72989330c 100644
>>>>>> --- a/drivers/pci/controller/dwc/pcie-designware.h
>>>>>> +++ b/drivers/pci/controller/dwc/pcie-designware.h
>>>>>> @@ -407,8 +407,10 @@ struct dw_pcie_ops {
>>>>>>  struct dw_pcie {
>>>>>>  	struct device		*dev;
>>>>>>  	void __iomem		*dbi_base;
>>>>>
>>>>>> +	phys_addr_t		dbi_phys_addr;
>>>>>>  	void __iomem		*dbi_base2;
>>>>>>  	void __iomem		*atu_base;
>>>>>> +	phys_addr_t		atu_phys_addr;
>>>>>
>>>>> What's the point in adding these fields to the generic DW PCIe private
>>>>> data if they are going to be used in the Qcom glue driver only?
>>>>>
>>>>> What about moving them to the qcom_pcie structure and initializing the
>>>>> fields in some place of the pcie-qcom.c driver?
>>>>>
>>>>> -Serge(y)
>>>>>
>>>>
>>>
>>>> These fields were in pcie-qcom.c driver in the v1 patch[1] and
>>>> Manivannan suggested to move these fields to 'struct dw_pcie' so that duplication
>>>> of resource fetching code 'platform_get_resource_byname()' can be avoided.
>>>>
>>>> [1] https://lore.kernel.org/linux-pci/a01404d2-2f4d-4fb8-af9d-3db66d39acf7@xxxxxxxxxxx/T/#mf9843386d57e9003de983e24e17de4d54314ff73
>>>
>>> Em, polluting the core driver structure with data not being used by
>>> the core driver but by the glue-code doesn't seem like a better
>>> alternative to additional platform_get_resource_byname() call in the
>>> glue-driver. I would have got back v1 version so to keep the core
>>> driver simpler. Bjorn?
>>>
>>
>> IDK how adding two fields which is very related to DWC code *pollutes* it. Since
>> there is already 'dbi_base', adding 'dbi_phys_addr' made sense to me even though
>> only glue drivers are using it. Otherwise, glue drivers have to duplicate the
>> platform_get_resource_byname() code which I find annoying.
> 
> I just explained why it was redundant:
> 1. adding the fields expands the core private data size for _all_
> platforms for no reason. (a few bytes but still)
> 2. the new fields aren't utilized by the core driver, but still
> defined in the core private data which is first confusing and
> second implicitly encourages the kernel developers to add another
> unused or even weakly-related fields in there.
> 3. the new fields utilized in a single glue-driver and there is a small
> chance they will be used in another ones. Another story would have
> been if we had them used in more than one glue-driver...
> 
> So from that perspective I find adding these fields to the driver core
> data less appropriate than duplicating the
> platform_get_resource_byname() call in a _single_ glue driver. It
> seems more reasonable to have them defined and utilized in the code
> that actually needs them, but not in the place that doesn't annoy you.)
> 
> Anyway I read your v1 command and did understand your point in the
> first place. That's why my question was addressed to Bjorn.
> 
> Please also note the resource::start field is of the resource_size_t
> type. So wherever the fields are added, it's better to have them
> defined of that type instead.
> 
> -Serge(y)
> 

Hi Bjorn,

Gentle ping for your feedback on the above discussed two approaches.

Thanks,
Prudhvi
>>
>> - Mani
>>
>> -- 
>> மணிவண்ணன் சதாசிவம்
>