linux-kernel - Re: [PATCH v2 5/6] misc: pci_endpoint_test: Do not request or allocate IRQs in probe

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Message-ID: <20210805112639.GA20438@lpieralisi>
Date:   Thu, 5 Aug 2021 12:26:39 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Arnd Bergmann <arnd@...db.de>, Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lokesh Vutla <lokeshvutla@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tom Joseph <tjoseph@...ence.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, nadeem@...ence.com
Subject: Re: [PATCH v2 5/6] misc: pci_endpoint_test: Do not request or
 allocate IRQs in probe

On Wed, Aug 04, 2021 at 07:32:44PM +0530, Kishon Vijay Abraham I wrote:
> Hi Lorenzo,
> 
> On 03/08/21 3:28 pm, Lorenzo Pieralisi wrote:
> > On Tue, Aug 03, 2021 at 01:19:31PM +0530, Kishon Vijay Abraham I wrote:
> >> Allocation of IRQ vectors and requesting IRQ is done as part of
> >> PCITEST_SET_IRQTYPE. Do not request or allocate IRQs in probe for
> >> AM654 and J721E so that the user space test script has better control
> >> of the devices for which the IRQs are configured. Since certain user
> >> space scripts could rely on allocation of IRQ vectors during probe,
> >> remove allocation of IRQs only for TI's K3 platform.
> >>
> >> Signed-off-by: Kishon Vijay Abraham I <kishon@...com>
> >> ---
> >>  drivers/misc/pci_endpoint_test.c | 19 +++++++++++++------
> >>  1 file changed, 13 insertions(+), 6 deletions(-)
> > 
> > I don't claim to understand the inner details of the endpoint test
> > device but it looks like this approach should be redesigned.
> > 
> > I don't believe using devices quirks is the best approach to
> > expose/remove a feature to userspace, this can soon become
> > unmaintenable.
> > 
> > Maybe you can elaborate a bit more on what the real issue is please ?
> 
> The actual reason for introducing this patch (affects only AM654 and
> J721E) is due to Errata ID #i2101 GIC: ITS Misbehavior
> (https://www.ti.com/lit/er/sprz455a/sprz455a.pdf). So if more than 5
> devices use GIC ITS simultaneously, GIC fails to raise interrupts.
> 
> Though this patch is not an actual workaround for the issue (the
> workaround is in GIC ITS driver provided in the errata document), it
> helps to keep testing PCIe RC/EP using pci-endpoint-test even when
> multiple pci-epf-test endpoint devices are connected (Normal test-setup
> having J721E-J721E back to back connection can support 21 pci-epf-test
> devices). So this patch lets user to individually enable interrupts for
> each of the devices and could disable after the interrupt test.
> 
> Since pci_endpoint_test is used only for testing PCIE RC/EP
> communication and pci-endpoint-test has already implemented
> PCITEST_SET_IRQTYPE for the userspace to enable interrupt, tried to not
> enable the interrupts of all the devices by default in the probe (for
> AM654 and J721E where this errata applies).

I understand - what I am asking is:

is it possible, instead of applying this patch, to make

pci_endpoint_test_alloc_irq_vectors() and pci_endpoint_test_request_irq()

fail in the target platforms instead of preventing to call them ?

My worry is that you may end up with more corner cases in the future
and peppering code with is_() calls to work around them which does
not look right.

Thanks,
Lorenzo

> Thanks,
> Kishon
> 
> > 
> > Thanks,
> > Lorenzo
> > 
> >> diff --git a/drivers/misc/pci_endpoint_test.c b/drivers/misc/pci_endpoint_test.c
> >> index c7ee34013485..9740f2a0e7cd 100644
> >> --- a/drivers/misc/pci_endpoint_test.c
> >> +++ b/drivers/misc/pci_endpoint_test.c
> >> @@ -79,6 +79,9 @@
> >>  #define PCI_DEVICE_ID_RENESAS_R8A774C0		0x002d
> >>  #define PCI_DEVICE_ID_RENESAS_R8A774E1		0x0025
> >>  
> >> +#define is_j721e_pci_dev(pdev)         \
> >> +		((pdev)->device == PCI_DEVICE_ID_TI_J721E)
> >> +
> >>  static DEFINE_IDA(pci_endpoint_test_ida);
> >>  
> >>  #define to_endpoint_test(priv) container_of((priv), struct pci_endpoint_test, \
> >> @@ -810,9 +813,11 @@ static int pci_endpoint_test_probe(struct pci_dev *pdev,
> >>  
> >>  	pci_set_master(pdev);
> >>  
> >> -	if (!pci_endpoint_test_alloc_irq_vectors(test, irq_type)) {
> >> -		err = -EINVAL;
> >> -		goto err_disable_irq;
> >> +	if (!(is_am654_pci_dev(pdev) || is_j721e_pci_dev(pdev))) {
> >> +		if (!pci_endpoint_test_alloc_irq_vectors(test, irq_type)) {
> >> +			err = -EINVAL;
> >> +			goto err_disable_irq;
> >> +		}
> >>  	}
> >>  
> >>  	for (bar = 0; bar < PCI_STD_NUM_BARS; bar++) {
> >> @@ -850,9 +855,11 @@ static int pci_endpoint_test_probe(struct pci_dev *pdev,
> >>  		goto err_ida_remove;
> >>  	}
> >>  
> >> -	if (!pci_endpoint_test_request_irq(test)) {
> >> -		err = -EINVAL;
> >> -		goto err_kfree_test_name;
> >> +	if (!(is_am654_pci_dev(pdev) || is_j721e_pci_dev(pdev))) {
> >> +		if (!pci_endpoint_test_request_irq(test)) {
> >> +			err = -EINVAL;
> >> +			goto err_kfree_test_name;
> >> +		}
> >>  	}
> >>  
> >>  	misc_device = &test->miscdev;
> >> -- 
> >> 2.17.1
> >>