linux-kernel - Re: [PATCH 1/4] PCI: Xilinx NWL: Fix, do not check for legacy status in while loop

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Date:   Mon, 23 Jan 2017 18:23:17 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>,
        bhelgaas@...gle.com, paul.gortmaker@...driver.com, robh@...nel.org,
        colin.king@...onical.com, linux-pci@...r.kernel.org
Cc:     michal.simek@...inx.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, rgummal@...inx.com, arnd@...db.de,
        Bharat Kumar Gogada <bharatku@...inx.com>
Subject: Re: [PATCH 1/4] PCI: Xilinx NWL: Fix, do not check for legacy status
 in while loop

On 21/01/17 11:11, Bharat Kumar Gogada wrote:
> - The legacy status register value for particular INTx becomes low
> only after DEASSERT_INTx is received.
> - Few End Points take time for sending DEASSERT_INTx, checking
> legacy status register in while loop causes invoking of EP
> handler continuosly until DEASSERT_INTx is received.
> 
> Signed-off-by: Bharat Kumar Gogada <bharatku@...inx.com>
> ---
>  drivers/pci/host/pcie-xilinx-nwl.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/host/pcie-xilinx-nwl.c b/drivers/pci/host/pcie-xilinx-nwl.c
> index 43eaa4a..c8b5a33 100644
> --- a/drivers/pci/host/pcie-xilinx-nwl.c
> +++ b/drivers/pci/host/pcie-xilinx-nwl.c
> @@ -342,9 +342,10 @@ static void nwl_pcie_leg_handler(struct irq_desc *desc)
>  
>  	chained_irq_enter(chip, desc);
>  	pcie = irq_desc_get_handler_data(desc);
> +	status = nwl_bridge_readl(pcie, MSGF_LEG_STATUS) &
> +				  MSGF_LEG_SR_MASKALL;
>  
> -	while ((status = nwl_bridge_readl(pcie, MSGF_LEG_STATUS) &
> -				MSGF_LEG_SR_MASKALL) != 0) {
> +	if (status != 0) {
>  		for_each_set_bit(bit, &status, INTX_NUM) {
>  			virq = irq_find_mapping(pcie->legacy_irq_domain,
>  						bit + 1);
> 

But even if you only handle the interrupt once, it is still asserted,
right? You exit the low-level exception handler, only to take the
interrupt immediately again. So what is the gain here?

As an aside, please add a cover letter to your patch series. It is
immensely useful as a summary of what is being done, as well as an
anchor for the patches themselves.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...