linux-kernel - RE: [PATCH] i2c: imx-lpi2c: change to PIO mode in system-wide suspend/resume progress

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Message-ID:
 <VI2PR04MB11147CEB59F804078F2136107E8D7A@VI2PR04MB11147.eurprd04.prod.outlook.com>
Date: Wed, 19 Nov 2025 06:02:45 +0000
From: Carlos Song <carlos.song@....com>
To: Frank Li <frank.li@....com>
CC: Aisheng Dong <aisheng.dong@....com>, "andi.shyti@...nel.org"
	<andi.shyti@...nel.org>, "shawnguo@...nel.org" <shawnguo@...nel.org>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>, "kernel@...gutronix.de"
	<kernel@...gutronix.de>, "festevam@...il.com" <festevam@...il.com>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-arm-kernel@...ts.infradead.org"
	<linux-arm-kernel@...ts.infradead.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] i2c: imx-lpi2c: change to PIO mode in system-wide
 suspend/resume progress



> -----Original Message-----
> From: Frank Li <frank.li@....com>
> Sent: Tuesday, November 18, 2025 11:58 PM
> To: Carlos Song <carlos.song@....com>
> Cc: Aisheng Dong <aisheng.dong@....com>; andi.shyti@...nel.org;
> shawnguo@...nel.org; s.hauer@...gutronix.de; kernel@...gutronix.de;
> festevam@...il.com; linux-i2c@...r.kernel.org; imx@...ts.linux.dev;
> linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] i2c: imx-lpi2c: change to PIO mode in system-wide
> suspend/resume progress
> 
> On Tue, Nov 18, 2025 at 03:18:37PM +0800, Carlos Song wrote:
> > If a system-wide suspend or resume transition is in progress. LPI2C
> > should use PIO to transfer data not DMA to avoid issue caused by not
> > ready DMA HW resource.
> 
> Currently there is no device link between the DMA engine and its DMA
> consumer, which allows the DMA engine to suspend before the consumer.
> 
> To avoid this, switch to PIO mode instead of DMA during suspend/resume so the
> transfer does not rely on the DMA engine’s state.
> 
> Notes: I suppose DMA engine suspend before LPI2C. Do you meet this or other
> reason cause DMA HW resource ready.
> 
> Not sure if below
> https://lore.kernel.org/dmaengine/20250912-v6-16-topic-dma-devlink-v1-0-4de
> bc2fbf901@...gutronix.de/
> can fix your problem.
> 
> Anyway, I think it is fine to use PIO at suspend to reduce dependence. But we
> need know why DMA HW is not ready.
> 
> Frank
> 
Hi, Frank

EDMA resume is in early stage and suspend is in late stage, but LPI2C resume and suspend are in NOIRQ stage.
So LPI2C resource become ready earlier than EDMA. When IRQ enabled, immediately slave will trigger I2C to read data and
the length meets the requirements for DMA usage, the DMA will be needed at this time. Within a very small time window,
EDMA is still not resumed. The root cause is from here.

dev link maybe useful in the same PM stage. But in different stage, I don’t know if it can help some.
Maybe it is better that DMA move PM stage to NOIRQ, but now there is no dev link for EDMA, the resume/suspend sequence between LPI2C and EDMA in NOIRQ
still cannot be completely guaranteed.

I totally agree your point: use PIO to reduce dependence.

If someday EDMA support dev link and move PM callback to NOIRQ stage both, this patch can be reverted I think.

Carlos
> >
> > Fixes: a09c8b3f9047 ("i2c: imx-lpi2c: add eDMA mode support for
> > LPI2C")
> > Signed-off-by: Carlos Song <carlos.song@....com>
> > ---
> >  drivers/i2c/busses/i2c-imx-lpi2c.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c
> > b/drivers/i2c/busses/i2c-imx-lpi2c.c
> > index 2a0962a0b441..5050e14a9919 100644
> > --- a/drivers/i2c/busses/i2c-imx-lpi2c.c
> > +++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
> > @@ -592,6 +592,13 @@ static bool is_use_dma(struct lpi2c_imx_struct
> *lpi2c_imx, struct i2c_msg *msg)
> >  	if (!lpi2c_imx->can_use_dma)
> >  		return false;
> >
> > +	/*
> > +	 * When system is in suspend process. LPI2C should use PIO to transfer
> data to
> > +	 * avoid issue caused by not ready DMA HW resource.
> > +	 */
> > +	if (pm_suspend_in_progress())
> > +		return false;
> > +
> >  	/*
> >  	 * When the length of data is less than I2C_DMA_THRESHOLD,
> >  	 * cpu mode is used directly to avoid low performance.
> > --
> > 2.34.1
> >