linux-kernel - Re: [PATCH v10 1/8] PCI: Add pcie_reset_flr to follow calling convention of other reset methods

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Date:   Wed, 28 Jul 2021 13:54:16 -0500
From:   Shanker R Donthineni <sdonthineni@...dia.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Amey Narkhede <ameynarkhede03@...il.com>
CC:     Bjorn Helgaas <bhelgaas@...gle.com>, <alex.williamson@...hat.com>,
        Raphael Norwitz <raphael.norwitz@...anix.com>,
        <linux-pci@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kw@...ux.com>, Sinan Kaya <okaya@...nel.org>,
        Len Brown <lenb@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH v10 1/8] PCI: Add pcie_reset_flr to follow calling
 convention of other reset methods

Hi Bjorn,

On 7/27/21 5:12 PM, Bjorn Helgaas wrote:
> External email: Use caution opening links or attachments
>
>
> On Fri, Jul 09, 2021 at 06:08:06PM +0530, Amey Narkhede wrote:
>> Add has_pcie_flr bitfield in struct pci_dev to indicate support for PCIe
>> FLR to avoid reading PCI_EXP_DEVCAP multiple times.
>>
>> Currently there is separate function pcie_has_flr() to probe if PCIe FLR
>> is supported by the device which does not match the calling convention
>> followed by reset methods which use second function argument to decide
>> whether to probe or not. Add new function pcie_reset_flr() that follows
>> the calling convention of reset methods.
>>
>> Signed-off-by: Amey Narkhede <ameynarkhede03@...il.com>
>> ---
>>  drivers/crypto/cavium/nitrox/nitrox_main.c |  4 +-
>>  drivers/pci/pci.c                          | 59 +++++++++++-----------
>>  drivers/pci/pcie/aer.c                     | 12 ++---
>>  drivers/pci/probe.c                        |  6 ++-
>>  drivers/pci/quirks.c                       |  9 ++--
>>  include/linux/pci.h                        |  3 +-
>>  6 files changed, 45 insertions(+), 48 deletions(-)
>>
>> diff --git a/drivers/crypto/cavium/nitrox/nitrox_main.c b/drivers/crypto/cavium/nitrox/nitrox_main.c
>> index facc8e6bc..15d6c8452 100644
>> --- a/drivers/crypto/cavium/nitrox/nitrox_main.c
>> +++ b/drivers/crypto/cavium/nitrox/nitrox_main.c
>> @@ -306,9 +306,7 @@ static int nitrox_device_flr(struct pci_dev *pdev)
>>               return -ENOMEM;
>>       }
>>
>> -     /* check flr support */
>> -     if (pcie_has_flr(pdev))
>> -             pcie_flr(pdev);
>> +     pcie_reset_flr(pdev, 0);
> I'm not really a fan of exposing the "probe" argument outside
> drivers/pci/.  I think this would be the only occurrence.  Is there a
> way to avoid that?
>
> Can we just make pcie_flr() do the equivalent of pcie_has_flr()
> internally?
>
I like your suggestion don't change the existing definition of pcie_has_flr()/pcie_flr()
and define a new function pcie_reset_flr() to fit into the reset framework. This way
no need to modify logic/drivers outside of driver/pci/xxx.

int pcie_reset_flr(struct pci_dev *dev, int probe)
{
        if (!pcie_has_flr(dev))
                return -ENOTTY;

        if (probe)
                return 0;

        return pcie_flr(dev);
}


And add a new patch to begging of the series for caching 'devcap' in pci_dev structure.

--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -333,6 +333,7 @@ struct pci_dev {
        struct rcec_ea  *rcec_ea;       /* RCEC cached endpoint association */
        struct pci_dev  *rcec;          /* Associated RCEC device */
 #endif
+       u32             devcap;         /* Cached PCIe device capabilities */
        u8              pcie_cap;       /* PCIe capability offset */
        u8              msi_cap;        /* MSI capability offset */
        u8              msix_cap;       /* MSI-X capability offset */


--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -31,6 +31,7 @@
 #include <linux/vmalloc.h>
 #include <asm/dma.h>
 #include <linux/aer.h>
+#include <linux/bitfield.h>
 #include "pci.h"

 DEFINE_MUTEX(pci_slot_mutex);
@@ -4630,13 +4631,10 @@ EXPORT_SYMBOL(pci_wait_for_pending_transaction);
  */
 bool pcie_has_flr(struct pci_dev *dev)
 {
-       u32 cap;
-
        if (dev->dev_flags & PCI_DEV_FLAGS_NO_FLR_RESET)
                return false;

-       pcie_capability_read_dword(dev, PCI_EXP_DEVCAP, &cap);
-       return cap & PCI_EXP_DEVCAP_FLR;
+       return !!FIELD_GET(PCI_EXP_DEVCAP_FLR, dev->devcap);
 }

--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -19,6 +19,7 @@
 #include <linux/hypervisor.h>
 #include <linux/irqdomain.h>
 #include <linux/pm_runtime.h>
+#include <linux/bitfield.h>
 #include "pci.h"

 #define CARDBUS_LATENCY_TIMER  176     /* secondary latency timer */
@@ -1498,8 +1499,8 @@ void set_pcie_port_type(struct pci_dev *pdev)
        pdev->pcie_cap = pos;
        pci_read_config_word(pdev, pos + PCI_EXP_FLAGS, &reg16);
        pdev->pcie_flags_reg = reg16;
-       pci_read_config_word(pdev, pos + PCI_EXP_DEVCAP, &reg16);
-       pdev->pcie_mpss = reg16 & PCI_EXP_DEVCAP_PAYLOAD;
+       pci_read_config_dword(pdev, pos + PCI_EXP_DEVCAP, &pdev->devcap);
+       pdev->pcie_mpss = FIELD_GET(PCI_EXP_DEVCAP_PAYLOAD, pdev->devcap);