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Date:   Fri, 13 Nov 2020 10:21:34 +0000
From:   Lee Jones <lee.jones@linaro.org>
To:     Tony Lindgren <tony@atomide.com>
Cc:     linux-kernel@vger.kernel.org,
        Carl Philipp Klemm <philipp@uvos.xyz>,
        Laxminath Kasam <lkasam@codeaurora.org>,
        Merlijn Wajer <merlijn@wizzup.org>,
        Mark Brown <broonie@kernel.org>, Pavel Machek <pavel@ucw.cz>,
        Sebastian Reichel <sre@kernel.org>,
        Tim Harvey <tharvey@gateworks.com>
Subject: Re: [PATCH] mfd: cpcap: Fix interrupt regression with regmap
 clear_ack
Message-ID: <20201113102134.GI3718728@dell>
References: <20201111170613.46057-1-tony@atomide.com>
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On Wed, 11 Nov 2020, Tony Lindgren wrote:

> With commit 3a6f0fb7b8eb ("regmap: irq: Add support to clear ack
> registers"), the cpcap interrupts are no longer getting acked properly
> leading to a very unresponsive device with CPUs fully loaded spinning
> in the threaded IRQ handlers.
> 
> To me it looks like the clear_ack commit above actually fixed a long
> standing bug in regmap_irq_thread() where we unconditionally acked the
> interrupts earlier without considering ack_invert. And the issue with
> cpcap started happening as we now also consider ack_invert.
> 
> Tim Harvey <tharvey@gateworks.com> tried to fix this issue earlier with
> "[PATCH v2] regmap: irq: fix ack-invert", but the reading of the ack
> register was considered unnecessary for just ack_invert, and we did not
> have clear_ack available yet. As the cpcap irqs worked both with and
> without ack_invert earlier because of the unconditional ack, the
> problem remained hidden until now.
> 
> Also, looks like the earlier v3.0.8 based Motorola Android Linux kernel
> does clear_ack style read-clear-write with "ireg_val & ~mreg_val" instead
> of just ack_invert style write. So let's switch cpcap to use clear_ack
> to fix the issue.
> 
> Fixes: 3a6f0fb7b8eb ("regmap: irq: Add support to clear ack registers")
> Cc: Carl Philipp Klemm <philipp@uvos.xyz>
> Cc: Laxminath Kasam <lkasam@codeaurora.org>
> Cc: Merlijn Wajer <merlijn@wizzup.org>
> Cc: Mark Brown <broonie@kernel.org>
> Cc: Pavel Machek <pavel@ucw.cz>
> Cc: Sebastian Reichel <sre@kernel.org>
> Cc: Tim Harvey <tharvey@gateworks.com>

It would be nice to have you review this Tim.

> Signed-off-by: Tony Lindgren <tony@atomide.com>
> ---
>  drivers/mfd/motorola-cpcap.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mfd/motorola-cpcap.c b/drivers/mfd/motorola-cpcap.c
> --- a/drivers/mfd/motorola-cpcap.c
> +++ b/drivers/mfd/motorola-cpcap.c
> @@ -97,7 +97,7 @@ static struct regmap_irq_chip cpcap_irq_chip[CPCAP_NR_IRQ_CHIPS] = {
>  		.ack_base = CPCAP_REG_MI1,
>  		.mask_base = CPCAP_REG_MIM1,
>  		.use_ack = true,
> -		.ack_invert = true,
> +		.clear_ack = true,
>  	},
>  	{
>  		.name = "cpcap-m2",
> @@ -106,7 +106,7 @@ static struct regmap_irq_chip cpcap_irq_chip[CPCAP_NR_IRQ_CHIPS] = {
>  		.ack_base = CPCAP_REG_MI2,
>  		.mask_base = CPCAP_REG_MIM2,
>  		.use_ack = true,
> -		.ack_invert = true,
> +		.clear_ack = true,
>  	},
>  	{
>  		.name = "cpcap1-4",
> @@ -115,7 +115,7 @@ static struct regmap_irq_chip cpcap_irq_chip[CPCAP_NR_IRQ_CHIPS] = {
>  		.ack_base = CPCAP_REG_INT1,
>  		.mask_base = CPCAP_REG_INTM1,
>  		.use_ack = true,
> -		.ack_invert = true,
> +		.clear_ack = true,
>  	},
>  };
>  

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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