linux-kernel - Re: [PATCH v3 4/5] misc: pci_endpoint_test: Remove global irq

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Message-ID: <fe8763e5-2d59-4b14-8a1c-b72e6df95520@socionext.com>
Date: Thu, 13 Feb 2025 19:21:59 +0900
From: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To: Niklas Cassel <cassel@...nel.org>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Krzysztof Wilczynski <kw@...ux.com>,
 Kishon Vijay Abraham I <kishon@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>,
 Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
 Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/5] misc: pci_endpoint_test: Remove global irq_type

Hi Niklas,

On 2025/02/11 1:30, Niklas Cassel wrote:
> On Mon, Feb 10, 2025 at 04:58:11PM +0900, Kunihiko Hayashi wrote:
>> The global variable "irq_type" preserves the current value of
>> ioctl(GET_IRQTYPE), however, it's enough to use test->irq_type.
>> Remove the variable, and replace with test->irq_type.
> 
> I think the commit message is missing the biggest point.
> 
> ioctl(SET_IRQTYPE) sets test->irq_type.
> PCITEST_WRITE/PCITEST_READ/PCITEST_COPY all use test->irq_type when
> writing the PCI_ENDPOINT_TEST_IRQ_TYPE register in test_reg_bar.
> 
> The endpoint function driver (pci-epf-test) will look at
> PCI_ENDPOINT_TEST_IRQ_TYPE register in test_reg_bar when determining
> which type of IRQ it should raise.
> 
> This means that the kernel module parameter is basically useless,
> since it is unused if anyone has called ioctl(SET_IRQTYPE).
> 
> Both the old pcitest.sh and the new pci_endpoint_test kselftest call
> ioctl(SET_IRQTYPE), so in practice the irq_type kernel module parameter
> is dead code.

Thank you for pointing out.

Surely, global "irq_type" is only used for return value of ioctl(GET_IRQTYPE).
It isn't used in the test case, and the test is completed with test->irq_type
and the register.

I'll add this point to the explanation.

>>
>> The ioctl(GET_IRQTYPE) returns an error if test->irq_type has
>> IRQ_TYPE_UNDEFINED.
>>
>> Suggested-by: Niklas Cassel <cassel@...nel.org>
>> Suggested-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
>> Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
>> ---
>>   drivers/misc/pci_endpoint_test.c | 13 ++++---------
>>   1 file changed, 4 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/misc/pci_endpoint_test.c
> b/drivers/misc/pci_endpoint_test.c
>> index 6a0972e7674f..8d98cd18634d 100644
>> --- a/drivers/misc/pci_endpoint_test.c
>> +++ b/drivers/misc/pci_endpoint_test.c
>> @@ -100,10 +100,6 @@ static bool no_msi;
>>   module_param(no_msi, bool, 0444);
>>   MODULE_PARM_DESC(no_msi, "Disable MSI interrupt in pci_endpoint_test");
> 
> Considering that you are removing the irq_type kernel module parameter,
> it doesn't make sense to keep the no_msi kernel module parameter IMO.
> 
> The exact same argument for why we are removing irq_type, can be made for
> no_msi.

Agreed.
Even if chip doesn't have MSI, test->irq_type starts with IRQ_TYPE_UNDEFINED
and will be changed with ioctl(SET_IRQTYPE).
"no_msi" can also be removed.

Thank you,

---
Best Regards
Kunihiko Hayashi