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

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Date:   Tue, 6 Dec 2022 05:30:13 +0000
From:   Bayi Cheng (程八意) 
        <bayi.cheng@...iatek.com>
To:     "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "ikjn@...omium.org" <ikjn@...omium.org>
CC:     "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "gch981213@...il.com" <gch981213@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>
Subject: Re: [PATCH v1] spi: spi-mtk-nor: Add recovery mechanism for dma read
 timeout

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@...iatek.com>
> > 
> > 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@...iatek.com>
> > ---
> > 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