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;
prev parent reply other threads:[~2021-07-08 2:03 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]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=95d72396-ccab-8550-806a-1b63ec383f80@alliedtelesis.co.nz \
--to=chris.packham@alliedtelesis.co.nz \
--cc=Hamish.Martin@alliedtelesis.co.nz \
--cc=linux-i2c@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=wsa@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).