netdev - Re: [PATCH v17 02/22] sfc: add cxl support

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Message-ID: <f56886cd-ca42-459a-87d7-eb3f472e88b4@amd.com>
Date: Mon, 30 Jun 2025 15:55:39 +0100
From: Alejandro Lucero Palau <alucerop@....com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 alejandro.lucero-palau@....com
Cc: linux-cxl@...r.kernel.org, netdev@...r.kernel.org,
 dan.j.williams@...el.com, edward.cree@....com, davem@...emloft.net,
 kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com,
 dave.jiang@...el.com, Edward Cree <ecree.xilinx@...il.com>,
 Alison Schofield <alison.schofield@...el.com>
Subject: Re: [PATCH v17 02/22] sfc: add cxl support


On 6/30/25 15:52, Alejandro Lucero Palau wrote:
>
> On 6/25/25 17:37, Jonathan Cameron wrote:
>> On Tue, 24 Jun 2025 15:13:35 +0100
>> <alejandro.lucero-palau@....com> wrote:
>>
>>> From: Alejandro Lucero <alucerop@....com>
>>>
>>> Add CXL initialization based on new CXL API for accel drivers and make
>>> it dependent on kernel CXL configuration.
>>>
>>> Signed-off-by: Alejandro Lucero <alucerop@....com>
>>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>>> Acked-by: Edward Cree <ecree.xilinx@...il.com>
>>> Reviewed-by: Alison Schofield <alison.schofield@...el.com>
>> Hi Alejandro,
>>
>> I think I'm missing something with respect to the relative life times.
>> Throwing one devm_ call into the middle of a probe is normally a recipe
>> for at least hard to read code, if not actual bugs.  It should be done
>> with care and accompanied by at least a comment.
>
>
> Hi Jonathan,
>
>
> I agree devm_* being harder in general and prone to some subtle 
> problems, but I can not see an issue here apart from the objects kept 
> until device unbinding. But I think adding some comment can help.
>
>
> <snip>
>
>> +
>> +    dvsec = pci_find_dvsec_capability(pci_dev, PCI_VENDOR_ID_CXL,
>> +                      CXL_DVSEC_PCIE_DEVICE);
>> +    if (!dvsec)
>> +        return 0;
>> +
>> +    pci_dbg(pci_dev, "CXL_DVSEC_PCIE_DEVICE capability found\n");
>> +
>> +    /* Create a cxl_dev_state embedded in the cxl struct using cxl 
>> core api
>> +     * specifying no mbox available.
>> +     */
>> +    cxl = devm_cxl_dev_state_create(&pci_dev->dev, CXL_DEVTYPE_DEVMEM,
>> +                    pci_dev->dev.id, dvsec, struct efx_cxl,
>> +                    cxlds, false);
>> The life time of this will outlast everything else in the efx driver.
>> Is that definitely safe to do?  Mostly from a reviewability and 
>> difficulty
>> of reasoning we avoid such late releasing of resources.
>>
>> Perhaps add to the comment before this call what you are doing to 
>> ensure that
>> it is fine to release this after everything in efx_pci_remove()
>>
>> Or wrap it up in a devres group and release that group in 
>> efx_cxl_exit().
>>
>> See devres_open_group(), devres_release_group()
>>
>>
>
> As I said above, I can not see a problem here, but maybe to explicitly 
> managed those resources with a devres group makes it simpler, so I 
> think it is a good advice to follow.
>
>
> Thanks!
>
>

FWIW, I just want to add that although I agree with this, it is somehow 
counterintuitive to me as the goal of devm is to avoid to care about 
when to release those allocations.