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

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Message-ID: <1a6ba55b-3077-4db2-a6cf-c7dc96619c94@amd.com>
Date: Mon, 30 Jun 2025 15:52:27 +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 6/25/25 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!