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From: Chris Packham <Chris.Packham@alliedtelesis.co.nz>
To: "wsa@kernel.org" <wsa@kernel.org>,
	Hamish Martin <Hamish.Martin@alliedtelesis.co.nz>
Cc: "linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] i2c: mpc: Restore reread of I2C status register
Date: Thu, 8 Jul 2021 02:03:41 +0000	[thread overview]
Message-ID: <95d72396-ccab-8550-806a-1b63ec383f80@alliedtelesis.co.nz> (raw)
In-Reply-To: <20210702032724.4370-1-chris.packham@alliedtelesis.co.nz>


On 2/07/21 3:27 pm, Chris Packham wrote:
> Prior to commit 1538d82f4647 ("i2c: mpc: Interrupt driven transfer") the
> old interrupt handler would reread MPC_I2C_SR after checking the CSR_MIF
> bit. When the driver was re-written this was removed as it seemed
> unnecessary. However as it turns out this is necessary for i2c devices
> which do clock stretching otherwise we end up thinking the bus is still
> busy when processing the interrupt.
>
> Fixes: 1538d82f4647 ("i2c: mpc: Interrupt driven transfer")
> Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>

Just a heads up that this hasn't totally fixed the issue. Just made it 
less likely to occur. I'm now wondering if we should be treating MCF as 
a busy bit and waiting for it to clear (with approrpriate timeouts) 
instead of just flagging an error immediately.

> ---
>   drivers/i2c/busses/i2c-mpc.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/drivers/i2c/busses/i2c-mpc.c b/drivers/i2c/busses/i2c-mpc.c
> index dcca9c2396db..6d5014ebaab5 100644
> --- a/drivers/i2c/busses/i2c-mpc.c
> +++ b/drivers/i2c/busses/i2c-mpc.c
> @@ -635,6 +635,8 @@ static irqreturn_t mpc_i2c_isr(int irq, void *dev_id)
>   
>   	status = readb(i2c->base + MPC_I2C_SR);
>   	if (status & CSR_MIF) {
> +		/* Read again to allow register to stabilise */
> +		status = readb(i2c->base + MPC_I2C_SR);
>   		writeb(0, i2c->base + MPC_I2C_SR);
>   		mpc_i2c_do_intr(i2c, status);
>   		return IRQ_HANDLED;

      parent reply	other threads:[~2021-07-08  2:04 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-02  3:27 [PATCH] i2c: mpc: Restore reread of I2C status register Chris Packham
2021-07-02  7:53 ` Wolfram Sang
2021-07-08  2:03 ` Chris Packham [this message]

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