Subject: Re: [PATCH kernel v3 06/22] powerpc/powernv: Detach npu struct from pnv_phb

From: Alistair Popple <[email-masked]>
Date: Wed, 14 Nov 2018 15:28:36 +1100

Hi Alexey,

On Tuesday, 13 November 2018 7:28:07 PM AEDT Alexey Kardashevskiy wrote:
>  static struct npu *npdev_to_npu(struct pci_dev *npdev)
>  {
> -	struct pnv_phb *nphb;
> +	struct pci_controller *hose = pci_bus_to_host(npdev->bus);
> +	struct npu *npu;
> 
> -	nphb = pci_bus_to_host(npdev->bus)->private_data;
> +	list_for_each_entry(npu, &npu2_devices, next)

This is called from the ATSD path which is (or at least has been) quite a 
performance critical path so searching through all the NPUs in a list may be 
problematic.

I guess currently it wont make any practical difference as we only ever have 2 
NPUs, but in future they may get divided into more logical NPUs. Would it be 
possible to store a back-pointer somewhere so we can avoid the lookup?

> +		if (hose == npu->hose)
> +			return npu;
> 
> -	return &nphb->npu;
> +	WARN_ON_ONCE(1);
> +	return NULL;
>  }
> 
>  /* Maximum number of nvlinks per npu */
> @@ -505,6 +531,9 @@ static void acquire_atsd_reg(struct npu_context
> *npu_context, continue;
> 
>  			npu = npdev_to_npu(npdev);
> +			if (!npu)
> +				continue;
> +
>  			mmio_atsd_reg[i].npu = npu;
>  			mmio_atsd_reg[i].reg = get_mmio_atsd_reg(npu);
>  			while (mmio_atsd_reg[i].reg < 0) {
> @@ -701,6 +730,8 @@ struct npu_context *pnv_npu2_init_context(struct pci_dev
> *gpdev,
> 
>  	nphb = pci_bus_to_host(npdev->bus)->private_data;
>  	npu = npdev_to_npu(npdev);
> +	if (!npu)
> +		return ERR_PTR(-ENODEV);
> 
>  	/*
>  	 * Setup the NPU context table for a particular GPU. These need to be
> @@ -821,6 +852,8 @@ void pnv_npu2_destroy_context(struct npu_context
> *npu_context,
> 
>  	nphb = pci_bus_to_host(npdev->bus)->private_data;
>  	npu = npdev_to_npu(npdev);
> +	if (!npu)
> +		return;
>  	nvlink_dn = of_parse_phandle(npdev->dev.of_node, "ibm,nvlink", 0);
>  	if (WARN_ON(of_property_read_u32(nvlink_dn, "ibm,npu-link-index",
>  							&nvlink_index)))
> @@ -898,9 +931,15 @@ int pnv_npu2_init(struct pnv_phb *phb)
>  	struct pci_dev *gpdev;
>  	static int npu_index;
>  	uint64_t rc = 0;
> +	struct pci_controller *hose = phb->hose;
> +	struct npu *npu;
> +	int ret;
> 
> -	phb->npu.nmmu_flush =
> -		of_property_read_bool(phb->hose->dn, "ibm,nmmu-flush");
> +	npu = kzalloc(sizeof(*npu), GFP_KERNEL);
> +	if (!npu)
> +		return -ENOMEM;
> +
> +	npu->nmmu_flush = of_property_read_bool(hose->dn, "ibm,nmmu-flush");
>  	for_each_child_of_node(phb->hose->dn, dn) {
>  		gpdev = pnv_pci_get_gpu_dev(get_pci_dev(dn));
>  		if (gpdev) {
> @@ -914,18 +953,31 @@ int pnv_npu2_init(struct pnv_phb *phb)
>  		}
>  	}
> 
> -	for (i = 0; !of_property_read_u64_index(phb->hose->dn, "ibm,mmio-atsd",
> +	for (i = 0; !of_property_read_u64_index(hose->dn, "ibm,mmio-atsd",
>  							i, &mmio_atsd); i++)
> -		phb->npu.mmio_atsd_regs[i] = ioremap(mmio_atsd, 32);
> +		npu->mmio_atsd_regs[i] = ioremap(mmio_atsd, 32);
> 
> -	pr_info("NPU%lld: Found %d MMIO ATSD registers", phb->opal_id, i);
> -	phb->npu.mmio_atsd_count = i;
> -	phb->npu.mmio_atsd_usage = 0;
> +	pr_info("NPU%d: Found %d MMIO ATSD registers", hose->global_number, i);
> +	npu->mmio_atsd_count = i;
> +	npu->mmio_atsd_usage = 0;
>  	npu_index++;
> -	if (WARN_ON(npu_index >= NV_MAX_NPUS))
> -		return -ENOSPC;
> +	if (WARN_ON(npu_index >= NV_MAX_NPUS)) {
> +		ret = -ENOSPC;
> +		goto fail_exit;
> +	}
>  	max_npu2_index = npu_index;
> -	phb->npu.index = npu_index;
> +	npu->index = npu_index;
> +	npu->hose = hose;
> +
> +	list_add(&npu->next, &npu2_devices);

Guess we don't need any locking here as the list gets setup once during boot 
long before loading the driver and is never modified right?

- Alistair

>  	return 0;
> +
> +fail_exit:
> +	for (i = 0; i < npu->mmio_atsd_count; ++i)
> +		iounmap(npu->mmio_atsd_regs[i]);
> +
> +	kfree(npu);
> +
> +	return ret;
>  }