Re: [PATCH v1] spi: spi-mtk-nor: Add recovery mechanism for dma read timeout

From: Bayi Cheng (程八意)
Date: Tue Dec 06 2022 - 00:30:39 EST


On Mon, 2022-12-05 at 15:01 +0100, AngeloGioacchino Del Regno wrote:
> Il 05/12/22 09:24, Bayi Cheng ha scritto:
> > From: bayi cheng <bayi.cheng@xxxxxxxxxxxx>
> >
> > The state machine of MTK spi nor controller may be disturbed by
> > some
> > glitch signals from the relevant BUS during dma read, Although the
> > possibility of causing the dma read to fail is next to nothing,
> > However, if error-handling is not implemented, which makes the
> > feature
> > somewhat risky.
> >
> > Add an error-handling mechanism here, reset the state machine and
> > re-read the data when an error occurs.
> >
> > Signed-off-by: bayi cheng <bayi.cheng@xxxxxxxxxxxx>
> > ---
> > Change in v1:
> > -Reset the state machine when dma read fails and read again.
> > ---
> > ---
> > drivers/spi/spi-mtk-nor.c | 16 +++++++++++++++-
> > 1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/spi/spi-mtk-nor.c b/drivers/spi/spi-mtk-nor.c
> > index d167699a1a96..c77d79da9a4c 100644
> > --- a/drivers/spi/spi-mtk-nor.c
> > +++ b/drivers/spi/spi-mtk-nor.c
> > @@ -80,6 +80,9 @@
> > #define MTK_NOR_REG_DMA_FADR 0x71c
> > #define MTK_NOR_REG_DMA_DADR 0x720
> > #define MTK_NOR_REG_DMA_END_DADR 0x724
> > +#define MTK_NOR_REG_CG_DIS 0x728
> > +#define MTK_NOR_SFC_SW_RST BIT(2)
> > +
> > #define MTK_NOR_REG_DMA_DADR_HB 0x738
> > #define MTK_NOR_REG_DMA_END_DADR_HB 0x73c
> >
> > @@ -616,7 +619,18 @@ static int mtk_nor_exec_op(struct spi_mem
> > *mem, const struct spi_mem_op *op)
> > mtk_nor_set_addr(sp, op);
> > return mtk_nor_read_pio(sp, op);
> > } else {
> > - return mtk_nor_read_dma(sp, op);
> > + ret = mtk_nor_read_dma(sp, op);
> > + if (ret) {
> > + dev_err(sp->dev, "try to read
> > again\n");
> > + mtk_nor_rmw(sp, MTK_NOR_REG_CG_DIS, 0,
> > MTK_NOR_SFC_SW_RST);
> > + mb(); /* flush previous writes */
> > + mtk_nor_rmw(sp, MTK_NOR_REG_CG_DIS,
> > MTK_NOR_SFC_SW_RST, 0);
> > + mb(); /* flush previous writes */
> > + writel(MTK_NOR_ENABLE_SF_CMD, sp->base
> > + MTK_NOR_REG_WP);
>
> From what I understand, you're introducing a way to perform a
> flush+reset on
> the controller.
>
> At this point, I'd put that in a separate function like
> `mtk_nor_reset()`, as
> to both increase readability and to possibly reuse it somewhere else
> in the
> future, if needed.
>
> So this would become...
>
> } else {
> ret = mtk_nor_read_dma(sp, op);
> if (unlikely(ret)) {
> /* Handle rare bus glitch */
> mtk_nor_reset(sp);
> mtk_nor_setup_bus(sp, op);
> return mtk_nor_read_dma(sp, op);
> }
> return ret;
> }
>
> ...or something alike :-)
>
> Regards,
> Angelo
>
Hi Angelo,

Thanks for your comments! I will fix it in the next patch.

Regards,
Bayi