linux-kernel - Re: [PATCH v4 2/7] PCI/ATS: Initialize PRI in pci_ats

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Date:   Thu, 1 Aug 2019 14:21:07 -0700
From:   sathyanarayanan kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Keith Busch <kbusch@...nel.org>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, ashok.raj@...el.com,
        keith.busch@...el.com
Subject: Re: [PATCH v4 2/7] PCI/ATS: Initialize PRI in pci_ats_init()

Hi Keith,

Thanks for the review.

On 8/1/19 2:09 PM, Keith Busch wrote:
> On Wed, Jul 03, 2019 at 01:46:19PM -0700, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
>> +#ifdef CONFIG_PCI_PRI
>> +static void pci_pri_init(struct pci_dev *pdev)
>> +{
>> +	u32 max_requests;
>> +	int pos;
>> +
>> +	/*
>> +	 * As per PCIe r4.0, sec 9.3.7.11, only PF is permitted to
>> +	 * implement PRI and all associated VFs can only use it.
>> +	 * Since PF already initialized the PRI parameters there is
>> +	 * no need to proceed further.
>> +	 */
>> +	if (pdev->is_virtfn)
>> +		return;
>> +
>> +	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
>> +	if (!pos)
>> +		return;
>> +
>> +	pci_read_config_dword(pdev, pos + PCI_PRI_MAX_REQ, &max_requests);
>> +
>> +	/*
>> +	 * Since PRI is a shared resource between PF and VF, we must not
>> +	 * configure Outstanding Page Allocation Quota as a per device
>> +	 * resource in pci_enable_pri(). So use maximum value possible
>> +	 * as default value.
>> +	 */
>> +	pci_write_config_dword(pdev, pos + PCI_PRI_ALLOC_REQ, max_requests);
>> +
>> +	pdev->pri_reqs_alloc = max_requests;
>> +	pdev->pri_cap = pos;
>> +}
>> +#endif
>> +
>>   void pci_ats_init(struct pci_dev *dev)
>>   {
>>   	int pos;
>> @@ -28,6 +62,10 @@ void pci_ats_init(struct pci_dev *dev)
>>   		return;
>>   
>>   	dev->ats_cap = pos;
>> +
>> +#ifdef CONFIG_PCI_PRI
>> +	pci_pri_init(dev);
>> +#endif
>>   }
> Rather than surround the call to pci_pri_init() with the #ifdef, you
> should provide an empty function implementation when CONFIG_PCI_PRI is
> not defined. Same thing for the next patch adding PASID.
This function is defined and used in the same file (ats.c). Is there any 
advantage in defining an empty function ? But if this is the recommended 
approach, I can make the necessary changes. Please confirm.
>
-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer