linux-kernel - Re: [PATCH v5 5/7] vfio/nvgrace-gpu: split the code to wait for GPU ready

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Message-ID: <20251124083249.3316c6e9.alex@shazbot.org>
Date: Mon, 24 Nov 2025 08:32:49 -0700
From: Alex Williamson <alex@...zbot.org>
To: <ankita@...dia.com>
Cc: <jgg@...pe.ca>, <yishaih@...dia.com>, <skolothumtho@...dia.com>,
 <kevin.tian@...el.com>, <aniketa@...dia.com>, <vsethi@...dia.com>,
 <mochs@...dia.com>, <Yunxiang.Li@....com>, <yi.l.liu@...el.com>,
 <zhangdongdong@...incomputing.com>, <avihaih@...dia.com>,
 <bhelgaas@...gle.com>, <peterx@...hat.com>, <pstanner@...hat.com>,
 <apopple@...dia.com>, <kvm@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <cjia@...dia.com>, <kwankhede@...dia.com>,
 <targupta@...dia.com>, <zhiw@...dia.com>, <danw@...dia.com>,
 <dnigam@...dia.com>, <kjaju@...dia.com>
Subject: Re: [PATCH v5 5/7] vfio/nvgrace-gpu: split the code to wait for GPU
 ready

On Mon, 24 Nov 2025 11:59:24 +0000
<ankita@...dia.com> wrote:

> From: Ankit Agrawal <ankita@...dia.com>
> 
> Split the function that check for the GPU device being ready on
> the probe.
> 
> Move the code to wait for the GPU to be ready through BAR0 register
> reads to a separate function. This would help reuse the code.
> 
> Signed-off-by: Ankit Agrawal <ankita@...dia.com>
> ---
>  drivers/vfio/pci/nvgrace-gpu/main.c | 33 ++++++++++++++++++-----------
>  1 file changed, 21 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/vfio/pci/nvgrace-gpu/main.c b/drivers/vfio/pci/nvgrace-gpu/main.c
> index c84c01954c9e..3e45b8bd1a89 100644
> --- a/drivers/vfio/pci/nvgrace-gpu/main.c
> +++ b/drivers/vfio/pci/nvgrace-gpu/main.c
> @@ -130,6 +130,24 @@ static void nvgrace_gpu_close_device(struct vfio_device *core_vdev)
>  	vfio_pci_core_close_device(core_vdev);
>  }
>  
> +static int nvgrace_gpu_wait_device_ready(void __iomem *io)
> +{
> +	unsigned long timeout = jiffies + msecs_to_jiffies(POLL_TIMEOUT_MS);
> +	int ret = -ETIME;
> +
> +	do {
> +		if ((ioread32(io + C2C_LINK_BAR0_OFFSET) == STATUS_READY) &&
> +		    (ioread32(io + HBM_TRAINING_BAR0_OFFSET) == STATUS_READY)) {
> +			ret = 0;
> +			goto ready_check_exit;
> +		}
> +		msleep(POLL_QUANTUM_MS);
> +	} while (!time_after(jiffies, timeout));
> +
> +ready_check_exit:
> +	return ret;
> +}
> +
>  static vm_fault_t nvgrace_gpu_vfio_pci_huge_fault(struct vm_fault *vmf,
>  						  unsigned int order)
>  {
> @@ -930,9 +948,8 @@ static bool nvgrace_gpu_has_mig_hw_bug(struct pci_dev *pdev)
>   * Ensure that the BAR0 region is enabled before accessing the
>   * registers.
>   */
> -static int nvgrace_gpu_wait_device_ready(struct pci_dev *pdev)
> +static int nvgrace_gpu_probe_check_device_ready(struct pci_dev *pdev)
>  {
> -	unsigned long timeout = jiffies + msecs_to_jiffies(POLL_TIMEOUT_MS);
>  	void __iomem *io;
>  	int ret = -ETIME;
>  
> @@ -950,16 +967,8 @@ static int nvgrace_gpu_wait_device_ready(struct pci_dev *pdev)
>  		goto iomap_exit;
>  	}
>  
> -	do {
> -		if ((ioread32(io + C2C_LINK_BAR0_OFFSET) == STATUS_READY) &&
> -		    (ioread32(io + HBM_TRAINING_BAR0_OFFSET) == STATUS_READY)) {
> -			ret = 0;
> -			goto reg_check_exit;
> -		}
> -		msleep(POLL_QUANTUM_MS);
> -	} while (!time_after(jiffies, timeout));
> +	ret = nvgrace_gpu_wait_device_ready(io);

I think you're inadvertently fixing a bug here too.  The ret
initialization to -ETIME is immediately clobbered by
pci_enable_device(), so exceeding the timeout would never generate an
error.  Now it will:

Fixes: d85f69d520e6 ("vfio/nvgrace-gpu: Check the HBM training and C2C link status")

Also we should remove the ret initialization.  Otherwise the series
LGTM.  Thanks,

Alex

>  
> -reg_check_exit:
>  	pci_iounmap(pdev, io);
>  iomap_exit:
>  	pci_release_selected_regions(pdev, 1 << 0);
> @@ -976,7 +985,7 @@ static int nvgrace_gpu_probe(struct pci_dev *pdev,
>  	u64 memphys, memlength;
>  	int ret;
>  
> -	ret = nvgrace_gpu_wait_device_ready(pdev);
> +	ret = nvgrace_gpu_probe_check_device_ready(pdev);
>  	if (ret)
>  		return ret;
>