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andi.shyti@kernel.org; > > shawnguo@kernel.org; s.hauer@pengutronix.de; kernel@pengutronix.de; > > festevam@gmail.com; linux-i2c@vger.kernel.org; imx@lists.linux.dev; > > linux-arm-kernel@lists.infradead.org; linux-kernel@vger.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@pengutronix.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. Put these information to commit message. Frank > > 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 > > > --- > > > 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 > > >