Re: [PATCH v5 2/2] i2c: spacemit: introduce pio for k1

From: Troy Mitchell <troy.mitchell@linux.spacemit.com>
To: Alex Elder <elder@riscstar.com>,
	Troy Mitchell <troy.mitchell@linux.spacemit.com>,
	Andi Shyti <andi.shyti@kernel.org>, Yixun Lan <dlan@gentoo.org>,
	Aurelien Jarno <aurelien@aurel32.net>,
	Michael Opdenacker <michael.opdenacker@rootcommit.com>,
	Troy Mitchell <troymitchell988@gmail.com>
Cc: linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-riscv@lists.infradead.org, spacemit@lists.linux.dev
Subject: Re: [PATCH v5 2/2] i2c: spacemit: introduce pio for k1
Date: Mon, 29 Dec 2025 10:07:35 +0800	[thread overview]
Message-ID: <6D29D0765AB5632A+aVHiZ9Wph0hNzqDY@kernel.org> (raw)
In-Reply-To: <86c5e338-e630-4933-a123-cfa1201495ed@riscstar.com>

> > @@ -474,6 +608,11 @@ static void spacemit_i2c_calc_timeout(struct spacemit_i2c_dev *i2c)
> >   	unsigned long timeout;
> >   	int idx = 0, cnt = 0;
> > +	if (i2c->use_pio) {
> > +		i2c->adapt.timeout = msecs_to_jiffies(SPACEMIT_WAIT_TIMEOUT);
> 
> Again, why is a rough 1000 millisecond timeout OK for PIO, while a
> fairly precise timeout value based on the number of bytes to be
> transferred and the transfer bit rate computed for interrupt mode?
Sorry I didn't see this.

In interrupt-driven mode we wait for a single completion event, so the
timeout needs to reflect the worst-case transfer duration to avoid
spurious timeouts.
In PIO mode the loop is driven by FIFO/status progress, and the timeout
is only a safeguard against a stalled bus rather than an exact transfer
time.
Therefore a simple conservative value is sufficient there.

                                  - Troy

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