linux-kernel - Re: [RFC PATCH v2 9/9] fpga: dfl: fix kernel warning on port release/assign for SRIOV

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Message-ID: <ZifVYiMgssOFjM17@yilunxu-OptiPlex-7050>
Date: Tue, 23 Apr 2024 23:36:02 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Peter Colberg <peter.colberg@...el.com>
Cc: Wu Hao <hao.wu@...el.com>, Tom Rix <trix@...hat.com>,
	Moritz Fischer <mdf@...nel.org>, Xu Yilun <yilun.xu@...el.com>,
	linux-fpga@...r.kernel.org, linux-kernel@...r.kernel.org,
	Russ Weight <russ.weight@...ux.dev>,
	Marco Pagani <marpagan@...hat.com>,
	Matthew Gerlach <matthew.gerlach@...ux.intel.com>,
	Russ Weight <russell.h.weight@...el.com>
Subject: Re: [RFC PATCH v2 9/9] fpga: dfl: fix kernel warning on port
 release/assign for SRIOV

On Tue, Apr 09, 2024 at 07:39:42PM -0400, Peter Colberg wrote:
> From: Xu Yilun <yilun.xu@...el.com>
> 
> DFL ports are registered as platform devices in PF mode. The port device
> should be removed from the host when the user wants to configure the
> port as a VF and pass through to a virtual machine. The FME device
> ioctls DFL_FPGA_FME_PORT_RELEASE/ASSIGN are designed for this purpose.
> 
> In the previous implementation, the port platform device is not completely
> destroyed on port release: it is removed from the system by
> platform_device_del(), but the platform device instance is retained.
> When the port assign ioctl is called, the platform device is added back by
> platform_device_add(), which conflicts with this comment of device_add():
> "Do not call this routine more than once for any device structure", and
> will cause a kernel warning at runtime.
> 
> This patch tries to completely unregister the port platform device on
> release and registers a new one on assign. But the main work is to remove
> the dependency on struct dfl_feature_platform_data for many internal DFL
> APIs. This structure holds many DFL enumeration infos for feature devices.
> Many DFL APIs are expected to work with these info even when the port
> platform device is unregistered. But with the change the platform_data will
> be freed in this case. So this patch introduces a new structure
> dfl_feature_dev_data for these APIs, which acts similarly to the previous
> dfl_feature_platform_data. The dfl_feature_platform_data then only needs a
> pointer to dfl_feature_dev_data to make the feature device driver work.
> 
> Signed-off-by: Xu Yilun <yilun.xu@...el.com>
> Signed-off-by: Russ Weight <russell.h.weight@...el.com>
> Signed-off-by: Peter Colberg <peter.colberg@...el.com>
> ---
> v2:
> - Split monolithic patch into series at request of maintainer
> - Substitute binfo->type for removed function feature_dev_id_type() in
>   parse_feature_irqs().
> - Return ERR_PTR(-ENOMEM) on !feature->params in
>   binfo_create_feature_dev_data().
> - Reorder cdev as first member of struct dfl_feature_platform_data
>   such that container_of() to obtain pdata evaluates to a no-op.
> - Align kernel-doc function name for __dfl_fpga_cdev_find_port_data().
> ---
>  drivers/fpga/dfl-afu-main.c |   9 +-
>  drivers/fpga/dfl-fme-br.c   |  24 +-
>  drivers/fpga/dfl-fme-main.c |   6 +-
>  drivers/fpga/dfl.c          | 430 +++++++++++++++++-------------------
>  drivers/fpga/dfl.h          |  86 +++++---
>  5 files changed, 281 insertions(+), 274 deletions(-)
> 
> diff --git a/drivers/fpga/dfl-afu-main.c b/drivers/fpga/dfl-afu-main.c
> index 42928cc7e42b..ead03b7aea70 100644
> --- a/drivers/fpga/dfl-afu-main.c
> +++ b/drivers/fpga/dfl-afu-main.c
> @@ -143,9 +143,8 @@ static int port_reset(struct platform_device *pdev)
>  	return ret;
>  }
>  
> -static int port_get_id(struct platform_device *pdev)
> +static int port_get_id(struct dfl_feature_dev_data *fdata)
>  {
> -	struct dfl_feature_dev_data *fdata = to_dfl_feature_dev_data(&pdev->dev);
>  	void __iomem *base;
>  
>  	base = dfl_get_feature_ioaddr_by_id(fdata, PORT_FEATURE_ID_HEADER);
> @@ -156,7 +155,8 @@ static int port_get_id(struct platform_device *pdev)
>  static ssize_t
>  id_show(struct device *dev, struct device_attribute *attr, char *buf)
>  {
> -	int id = port_get_id(to_platform_device(dev));
> +	struct dfl_feature_dev_data *fdata = to_dfl_feature_dev_data(dev);
> +	int id = port_get_id(fdata);

My quick idea is we go with these steps:
1. refactor struct dfl_feature_platform_data then replace all dev/pdev
   arguments with pdata when necessary.
2. factor out fdata from pdata, add fdata helpers.
3. massive pdata->fdata replacement.
4. delete all unused pdata helpers.

Please check if it is possible.

Thanks,
Yilun