netdev - Re: [RESEND PATCH V3 6/6] PCI: Enable 10-Bit tag support for PCIe RP devices

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Date:   Tue, 15 Jun 2021 11:08:05 +0800
From:   Dongdong Liu <liudongdong3@...wei.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     <helgaas@...nel.org>, <kw@...ux.com>, <linux-pci@...r.kernel.org>,
        <rajur@...lsio.com>, <hverkuil-cisco@...all.nl>,
        <linux-media@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: Re: [RESEND PATCH V3 6/6] PCI: Enable 10-Bit tag support for PCIe RP
 devices



On 2021/6/14 13:57, Christoph Hellwig wrote:
> On Sun, Jun 13, 2021 at 05:29:15PM +0800, Dongdong Liu wrote:
>> PCIe spec 5.0r1.0 section 2.2.6.2 implementation note, In configurations
>> where a Requester with 10-Bit Tag Requester capability needs to target
>> multiple Completers, one needs to ensure that the Requester sends 10-Bit
>> Tag Requests only to Completers that have 10-Bit Tag Completer capability.
>> So we enable 10-Bit Tag Requester for root port only when the devices
>> under the root port support 10-Bit Tag Completer.
>>
>> Signed-off-by: Dongdong Liu <liudongdong3@...wei.com>
>> ---
>>  drivers/pci/pcie/portdrv_pci.c | 75 ++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 75 insertions(+)
>>
>> diff --git a/drivers/pci/pcie/portdrv_pci.c b/drivers/pci/pcie/portdrv_pci.c
>> index c7ff1ee..baf413f 100644
>> --- a/drivers/pci/pcie/portdrv_pci.c
>> +++ b/drivers/pci/pcie/portdrv_pci.c
>> @@ -90,6 +90,78 @@ static const struct dev_pm_ops pcie_portdrv_pm_ops = {
>>  #define PCIE_PORTDRV_PM_OPS	NULL
>>  #endif /* !PM */
>>
>> +static int pci_10bit_tag_comp_support(struct pci_dev *dev, void *data)
>> +{
>> +	u8 *support = data;
>> +
>> +	if (*support == 0)
>> +		return 0;
>> +
>> +	if (!pci_is_pcie(dev)) {
>> +		*support = 0;
>> +		return 0;
>> +	}
>> +
>> +	/*
>> +	 * PCIe spec 5.0r1.0 section 2.2.6.2 implementation note.
>> +	 * For configurations where a Requester with 10-Bit Tag Requester
>> +	 * capability targets Completers where some do and some do not have
>> +	 * 10-Bit Tag Completer capability, how the Requester determines which
>> +	 * NPRs include 10-Bit Tags is outside the scope of this specification.
>> +	 * So we do not consider hotplug scenario.
>> +	 */
>> +	if (dev->is_hotplug_bridge) {
>> +		*support = 0;
>> +		return 0;
>> +	}
>> +
>> +	if (!(dev->pcie_devcap2 & PCI_EXP_DEVCAP2_10BIT_TAG_COMP)) {
>> +		*support = 0;
>> +		return 0;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static void pci_configure_rp_10bit_tag(struct pci_dev *dev)
>> +{
>> +	u8 support = 1;
>> +	struct pci_dev *pchild;
>> +
>> +	if (dev->subordinate == NULL)
>> +		return;
>> +
>> +	/* If no devices under the root port, no need to enable 10-Bit Tag. */
>> +	pchild = list_first_entry_or_null(&dev->subordinate->devices,
>> +					  struct pci_dev, bus_list);
>> +	if (pchild == NULL)
>> +		return;
>
> pchild is never used after this check, so this could be simplified to
> a list_empty(&dev->subordinate->devices).
Good point, will do.

Thanks,
Dongdong
> .
>