Re: [RFC PATCH v1] mtd: rawnand: meson: invalidate cache on polling ECC bit

[Miquel Raynal]

Hi Arseniy,

avkrasnov@xxxxxxxxxxxxxx wrote on Mon, 13 Mar 2023 10:36:11 +0300:

> Hello,
> 
> we reproduced this problem on one of our boards. It triggers very rare
> when 'usleep_range()' is present, but when sleeping is removed - it fires
> always. I suppose problem is with caching, as 'info_buf' memory is mapped by
> 'dma_map_single()'.

The fix looks really legitimate, indeed I get that the usleep_range()
might make it work most of the time but not always. Having this bit in
a DMA buf area is a bit strange. Well, the fix LGTM anyway.

> 
> Thanks, Arseniy
> 
> On 13.03.2023 10:32, Arseniy Krasnov wrote:
> > 'info_buf' memory is cached and driver polls ECC bit in it. This bit
> > is set by the NAND controller. If 'usleep_range()' returns before device
> > sets this bit, 'info_buf' will be cached and driver won't see update of
> > this bit and will loop forever.
> > 
> > Fixes: 8fae856c5350 ("mtd: rawnand: meson: add support for Amlogic NAND flash controller")
> > Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
> > ---
> >  drivers/mtd/nand/raw/meson_nand.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/mtd/nand/raw/meson_nand.c b/drivers/mtd/nand/raw/meson_nand.c
> > index 5ee01231ac4c..2c05c08a0eaf 100644
> > --- a/drivers/mtd/nand/raw/meson_nand.c
> > +++ b/drivers/mtd/nand/raw/meson_nand.c
> > @@ -176,6 +176,7 @@ struct meson_nfc {
> >  
> >  	dma_addr_t daddr;
> >  	dma_addr_t iaddr;
> > +	u32 info_bytes;
> >  
> >  	unsigned long assigned_cs;
> >  };
> > @@ -503,6 +504,7 @@ static int meson_nfc_dma_buffer_setup(struct nand_chip *nand, void *databuf,
> >  					 nfc->daddr, datalen, dir);
> >  			return ret;
> >  		}
> > +		nfc->info_bytes = infolen;
> >  		cmd = GENCMDIADDRL(NFC_CMD_AIL, nfc->iaddr);
> >  		writel(cmd, nfc->reg_base + NFC_REG_CMD);
> >  
> > @@ -520,8 +522,10 @@ static void meson_nfc_dma_buffer_release(struct nand_chip *nand,
> >  	struct meson_nfc *nfc = nand_get_controller_data(nand);
> >  
> >  	dma_unmap_single(nfc->dev, nfc->daddr, datalen, dir);
> > -	if (infolen)
> > +	if (infolen) {
> >  		dma_unmap_single(nfc->dev, nfc->iaddr, infolen, dir);
> > +		nfc->info_bytes = 0;
> > +	}
> >  }
> >  
> >  static int meson_nfc_read_buf(struct nand_chip *nand, u8 *buf, int len)
> > @@ -710,6 +714,8 @@ static void meson_nfc_check_ecc_pages_valid(struct meson_nfc *nfc,
> >  		usleep_range(10, 15);
> >  		/* info is updated by nfc dma engine*/
> >  		smp_rmb();
> > +		dma_sync_single_for_cpu(nfc->dev, nfc->iaddr, nfc->info_bytes,
> > +					DMA_FROM_DEVICE);
> >  		ret = *info & ECC_COMPLETE;
> >  	} while (!ret);
> >  }  


Thanks,
Miquèl