linux-kernel - Re: [PATCH v1 4/7] fpga: dfl: fix VF creation when ports have no local BAR space

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Date:   Fri, 18 Feb 2022 06:55:58 -0800
From:   Tom Rix <trix@...hat.com>
To:     "Zhang, Tianfei" <tianfei.zhang@...el.com>,
        "Wu, Hao" <hao.wu@...el.com>, "mdf@...nel.org" <mdf@...nel.org>,
        "Xu, Yilun" <yilun.xu@...el.com>,
        "linux-fpga@...r.kernel.org" <linux-fpga@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "corbet@....net" <corbet@....net>,
        Matthew Gerlach <matthew.gerlach@...ux.intel.com>
Subject: Re: [PATCH v1 4/7] fpga: dfl: fix VF creation when ports have no
 local BAR space


On 2/18/22 12:14 AM, Zhang, Tianfei wrote:
>
>> -----Original Message-----
>> From: Tom Rix <trix@...hat.com>
>> Sent: Tuesday, February 15, 2022 11:51 PM
>> To: Zhang, Tianfei <tianfei.zhang@...el.com>; Wu, Hao <hao.wu@...el.com>;
>> mdf@...nel.org; Xu, Yilun <yilun.xu@...el.com>; linux-fpga@...r.kernel.org;
>> linux-doc@...r.kernel.org; linux-kernel@...r.kernel.org
>> Cc: corbet@....net; Matthew Gerlach <matthew.gerlach@...ux.intel.com>
>> Subject: Re: [PATCH v1 4/7] fpga: dfl: fix VF creation when ports have no local
>> BAR space
>>
>>
>> On 2/14/22 3:26 AM, Tianfei zhang wrote:
>>> From: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
>>>
>>> When a port is not connected to the same PCIe endpoint as the FME, the
>>> port does not need to be released before being virtualized.  Fix VF
>>> creation code to handle this new use
>> Similar, how does this fit in with iofs, this looks like it would not be valid for the
>> existing cards
> IOFS introducing multiple methods for PR and AFU access.
> 1. Legacy Model.
> 2. Micro-Personas in AFU.
> 3. Multiple VFs per PR slot.
>
> For 1 and 2 model, there are 1:1 mapping between Port device and PR slot (or entire AFU). In virtualization,
> it should release the Port device firstly and then assign to VM. In this models, the DFL driver will track  that
> the number of port devices has released (cdev->released_port_num in dfl_fpga_cdev_config_ports_vf() function)
> are equal with the numbers of SRIOV or not. But in model 3, it has multiple VFs per PR slot, and assign the VF to VM
> without release the port device, so the tracking mechanism of cdev->released_port_num is not workable on new

If ->release_port_num is not workable, then it needs to be generalized.

Refactor to handle all the cases.

Tom

> model. This patch want to handle this new model during VF creation.
>
>>> case.
>>>
>>> Signed-off-by: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
>>> Signed-off-by: Tianfei Zhang <tianfei.zhang@...el.com>
>>> ---
>>>    drivers/fpga/dfl.c | 11 +++++++++--
>>>    1 file changed, 9 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/fpga/dfl.c b/drivers/fpga/dfl.c index
>>> 26f8cf890700..cfc539a656f0 100644
>>> --- a/drivers/fpga/dfl.c
>>> +++ b/drivers/fpga/dfl.c
>>> @@ -1705,15 +1705,22 @@
>> EXPORT_SYMBOL_GPL(dfl_fpga_cdev_config_ports_pf);
>>>    int dfl_fpga_cdev_config_ports_vf(struct dfl_fpga_cdev *cdev, int num_vfs)
>>>    {
>>>    	struct dfl_feature_platform_data *pdata;
>>> -	int ret = 0;
>>> +	int ret = 0, port_count = 0;
>>>
>>>    	mutex_lock(&cdev->lock);
>>> +
>>> +	list_for_each_entry(pdata, &cdev->port_dev_list, node) {
>>> +		if (pdata->dev)
>> This looks wrong,
>>
>> pdata->dev is dereferenced below, if there is a case were (!pdata->dev)
>> here there would be crash later.
>>
>>> +			continue;
>>> +		port_count++;
>> how does this work when only some of the ports are handled in the new way ?
> This code want to handle the " Multiple VFs per PR slot" model as I mentioned above.
> In new model, the port_count want to count that how many port devices have released.
> This code looks not good readability, I try to re-write it.
>
>> Tom
>>
>>> +	}
>>> +
>>>    	/*
>>>    	 * can't turn multiple ports into 1 VF device, only 1 port for 1 VF
>>>    	 * device, so if released port number doesn't match VF device number,
>>>    	 * then reject the request with -EINVAL error code.
>>>    	 */
>>> -	if (cdev->released_port_num != num_vfs) {
>>> +	if (port_count && cdev->released_port_num != num_vfs) {
>>>    		ret = -EINVAL;
>>>    		goto done;
>>>    	}