linux-kernel - Re: [PATCH V7 02/15] PCI: Disable MSI for Tegra194 root port

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Date:   Wed, 22 May 2019 01:04:58 +0530
From:   Vidya Sagar <vidyas@...dia.com>
To:     Thierry Reding <thierry.reding@...il.com>
CC:     <lorenzo.pieralisi@....com>, <bhelgaas@...gle.com>,
        <robh+dt@...nel.org>, <mark.rutland@....com>,
        <jonathanh@...dia.com>, <kishon@...com>, <catalin.marinas@....com>,
        <will.deacon@....com>, <jingoohan1@...il.com>,
        <gustavo.pimentel@...opsys.com>, <mperttunen@...dia.com>,
        <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <kthota@...dia.com>,
        <mmaddireddy@...dia.com>, <sagar.tv@...il.com>
Subject: Re: [PATCH V7 02/15] PCI: Disable MSI for Tegra194 root port

On 5/21/2019 10:17 PM, Vidya Sagar wrote:
> On 5/21/2019 3:57 PM, Thierry Reding wrote:
>> On Fri, May 17, 2019 at 06:08:33PM +0530, Vidya Sagar wrote:
>>> Tegra194 rootports don't generate MSI interrupts for PME events and hence
>>> MSI needs to be disabled for them to avoid root ports service drivers
>>> registering their respective ISRs with MSI interrupt.
>>>
>>> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
>>> ---
>>> Changes since [v6]:
>>> * This is a new patch
>>>
>>>   drivers/pci/quirks.c | 14 ++++++++++++++
>>>   1 file changed, 14 insertions(+)
>>>
>>> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
>>> index 0f16acc323c6..28f9a0380df5 100644
>>> --- a/drivers/pci/quirks.c
>>> +++ b/drivers/pci/quirks.c
>>> @@ -2592,6 +2592,20 @@ DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_NVIDIA,
>>>               PCI_DEVICE_ID_NVIDIA_NVENET_15,
>>>               nvenet_msi_disable);
>>> +/*
>>> + * Tegra194's PCIe root ports don't generate MSI interrupts for PME events
>>> + * instead legacy interrupts are generated. Hence, to avoid service drivers
>>> + * registering their respective ISRs for MSIs, need to disable MSI interrupts
>>> + * for root ports.
>>> + */
>>> +static void disable_tegra194_rp_msi(struct pci_dev *dev)
>>> +{
>>> +    dev->no_msi = 1;
>>> +}
>>> +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_NVIDIA, 0x1ad0, disable_tegra194_rp_msi);
>>> +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_NVIDIA, 0x1ad1, disable_tegra194_rp_msi);
>>> +DECLARE_PCI_FIXUP_EARLY(PCI_VENDOR_ID_NVIDIA, 0x1ad2, disable_tegra194_rp_msi);
>>> +
>>
>> Later functions in this file seem to use a more consistent naming
>> pattern, according to which the name for this would become:
>>
>>     pci_quirk_nvidia_tegra194_disable_rp_msi
>>
>> Might be worth considering making this consistent.
>>
>> This could also be moved to the DWC driver to restrict this to where it
>> is needed. In either case, this seems like a good solution, so:
>>
>> Reviewed-by: Thierry Reding <treding@...dia.com>
>>
> Ok. I'll move it to DWC driver along with name change for the quirk API.
> 
I see that if quirk macros and API are present in pcie-tegra194.c file and driver is built
as a module, quirk API is not getting invoked by the system, whereas it gets invoked if driver
is built into kernel. Is this behavior expected? I think it is because of quirk API symbol
not available as part of global quirk symbol table when driver is built as a module?
for now, I'm going to keep quirk macros and API in pci/quirks.c file itself.