RE: [PATCH v2] i2c: imx-lpi2c: change to PIO mode in system-wide suspend/resume progress

[Carlos Song]

> -----Original Message-----
> From: Frank Li <frank.li@xxxxxxx>
> Sent: Thursday, November 20, 2025 11:40 PM
> To: Carlos Song <carlos.song@xxxxxxx>
> Cc: Aisheng Dong <aisheng.dong@xxxxxxx>; andi.shyti@xxxxxxxxxx;
> shawnguo@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx; kernel@xxxxxxxxxxxxxx;
> linux-i2c@xxxxxxxxxxxxxxx; imx@xxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2] i2c: imx-lpi2c: change to PIO mode in system-wide
> suspend/resume progress
> 
> On Thu, Nov 20, 2025 at 06:30:39PM +0800, Carlos Song wrote:
> > 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
> > LPI2C to read data and the length meets the requirements for DMA
> > usage, the DMA
> 
> "the length meets the requirements for DMA usage" is condition to trigger DMA,
> reader easily miss this and confuse.
> 
> > will be needed at this time. Within a very small time window, EDMA is
> > still not resumed.
> >
> > 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.
> 
> You can use AI help rephrase.
> 
> EDMA resume happens in the early stage and suspend in the late stage, while
> LPI2C resume and suspend run in the NOIRQ stage. This causes the LPI2C
> resources to become available earlier than EDMA. When IRQs are enabled, a
> slave device may immediately trigger LPI2C to read data. If the transfer length
> meets the DMA requirements, the driver will attempt to use EDMA even though
> EDMA may not yet be resumed.
> 
> Within this small timing window, EDMA is unavailable, leading to transfer
> failures. Force PIO mode for LPI2C during system suspend and resume
> transitions to reduce system dependency and avoid using an unready EDMA
> resource.
> 

Thank you Frank, I will send V3 according to this.

> Frank
> >
> > Fixes: a09c8b3f9047 ("i2c: imx-lpi2c: add eDMA mode support for
> > LPI2C")
> > Signed-off-by: Carlos Song <carlos.song@xxxxxxx>
> > ---
> >  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..d882126c1778 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;
> >
> > +	/*
> > +	 * A system-wide suspend or resume transition is in progress. LPI2C should
> use PIO to
> > +	 * transfer data to avoid issue caused by no 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
> >