linux-kernel - RE: [PATCH v2 1/2] PCI: Xilinx NWL: Modifying irq chip for legacy interrupts

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Date:   Mon, 30 Jan 2017 05:56:43 +0000
From:   Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
To:     Marc Zyngier <marc.zyngier@....com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "paul.gortmaker@...driver.com" <paul.gortmaker@...driver.com>,
        "robh@...nel.org" <robh@...nel.org>,
        "colin.king@...onical.com" <colin.king@...onical.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
CC:     "michal.simek@...inx.com" <michal.simek@...inx.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ravikiran Gummaluri <rgummal@...inx.com>,
        "arnd@...db.de" <arnd@...db.de>
Subject: RE: [PATCH v2 1/2] PCI: Xilinx NWL: Modifying irq chip for legacy
 interrupts

> The subject line is not very descriptive. How about "Enforce level
> triggering for legacy interrupts"?
> 
> On 25/01/17 08:52, Bharat Kumar Gogada wrote:
> > - Few wifi end points which only support legacy interrupts,
> > performs hardware reset functionalities after disabling interrupts
> > by invoking disable_irq and then re-enable using enable_irq, they
> > enable hardware interrupts first and then virtual irq line later.
> > - The legacy irq line goes low only after DEASSERT_INTx is
> > received.As the legacy irq line is high immediately after hardware
> > interrupts are enabled but virq of EP is still in disabled state
> > and EP handler is never executed resulting no DEASSERT_INTx.If dummy
> > irq chip is used, interrutps are not masked and system is
> 
>                     interrupts
> 
> > hanging with CPU stall.
> > - Adding irq chip functions instead of dummy irq chip for legacy
> > interrupts.
> > - Legacy interrupts are level sensitive, so using handle_level_irq
> > is more appropriate as it is masks interrupts until End point handles
> > interrupts and unmasks interrutps after End point handler is executed.
> 
>                          interrupts
> 
> >
> > Signed-off-by: Bharat Kumar Gogada <bharatku@...inx.com>
> > ---
> >  drivers/pci/host/pcie-xilinx-nwl.c | 36
> +++++++++++++++++++++++++++++++++++-
> >  1 file changed, 35 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/host/pcie-xilinx-nwl.c b/drivers/pci/host/pcie-xilinx-
> nwl.c
> > index 43eaa4a..6ac3e1d 100644
> > --- a/drivers/pci/host/pcie-xilinx-nwl.c
> > +++ b/drivers/pci/host/pcie-xilinx-nwl.c
> > @@ -395,10 +395,44 @@ static void nwl_pcie_msi_handler_low(struct
> irq_desc *desc)
> >  	chained_irq_exit(chip, desc);
> >  }
> >
> > +static void nwl_mask_leg_irq(struct irq_data *data)
> > +{
> > +	struct irq_desc *desc = irq_to_desc(data->irq);
> > +	struct nwl_pcie *pcie;
> > +	u32 mask;
> > +	u32 val;
> > +
> > +	pcie = irq_desc_get_chip_data(desc);
> > +	mask = 1 << (data->hwirq - 1);
> > +	val = nwl_bridge_readl(pcie, MSGF_LEG_MASK);
> > +	nwl_bridge_writel(pcie, (val & (~mask)), MSGF_LEG_MASK);
> 
> Oh please! Think of the following:
> 
> 	cpu0	cpu1
> 	read
> 		read
> 		write
> 	write
> 
> How can you make this reliable if you don't have any form of mutual
> exclusion that spans both mask and unmask, and ensures the atomicity of
> the RMW sequence?
> 
Agreed, will send with locks.