Re: [RFC] mmc: meson-gx: use memcpy_to/fromio for dram-access-quirk

[Robin Murphy]

On 2021-06-09 14:07, Neil Armstrong wrote:
> Hi,
>
> On 08/06/2021 17:50, Marek Szyprowski wrote:
> > Hi
> >
> > On 08.06.2021 17:33, Neil Armstrong wrote:
> > > It has been reported that usage of memcpy() to/from an iomem mapping is invalid,
> > > and and recent arm64 memcpy update [1] triggers a memory abort when dram-access-quirk
> > > is used on the G12A/G12B platforms.
> > >
> > > This adds a local sg_copy_to_buffer which makes usage of io versions of memcpy
> > > when dram-access-quirk is enabled.
> > >
> > > Fixes: acdc8e71d9bb ("mmc: meson-gx: add dram-access-quirk")
> > > Reported-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> > > Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
> > > Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
> > >
> > > [1] 285133040e6c ("arm64: Import latest memcpy()/memmove() implementation")
> > >
> > > Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
> > > ---
> > > Hi Ulf, Marek, Mark,
> > >
> > > I haven't tested the patch yet, but should fix issue reported at [2].
> >
> > Works fine here and fixed the issue.
> >
> > Tested-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
>
> Thanks, I'll need to rework to pass an __iomem pointer to memcpy_to/fromio so sparse doesn't scream anymore.

Hmm, might it be worth factoring out general sg_copy_{to,from}_iomem() 
helpers? From a quick grep I found at least mv_cesa_sg_copy() already 
doing essentially the same thing as meson_mmc_copy_buffer().

Robin.

> Neil
>
> > > Neil
> > >
> > > [2] https://lore.kernel.org/r/acb244ad-0759-5a96-c659-5c23003d3dcd@xxxxxxxxxxx
> > >
> > >    drivers/mmc/host/meson-gx-mmc.c | 48 ++++++++++++++++++++++++++++++---
> > >    1 file changed, 44 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/mmc/host/meson-gx-mmc.c b/drivers/mmc/host/meson-gx-mmc.c
> > > index b8b771b643cc..89ff6038092d 100644
> > > --- a/drivers/mmc/host/meson-gx-mmc.c
> > > +++ b/drivers/mmc/host/meson-gx-mmc.c
> > > @@ -742,6 +742,48 @@ static void meson_mmc_desc_chain_transfer(struct mmc_host *mmc, u32 cmd_cfg)
> > >    	writel(start, host->regs + SD_EMMC_START);
> > >    }
> > >    
> > > +/* local sg copy to buffer version with _to/fromio usage for dram_access_quirk */
> > > +static void meson_mmc_copy_buffer(struct meson_host *host, struct mmc_data *data,
> > > +				  size_t buflen, bool to_buffer)
> > > +{
> > > +	unsigned int sg_flags = SG_MITER_ATOMIC;
> > > +	struct scatterlist *sgl = data->sg;
> > > +	unsigned int nents = data->sg_len;
> > > +	struct sg_mapping_iter miter;
> > > +	void *buf = host->bounce_buf;
> > > +	unsigned int offset = 0;
> > > +
> > > +	if (to_buffer)
> > > +		sg_flags |= SG_MITER_FROM_SG;
> > > +	else
> > > +		sg_flags |= SG_MITER_TO_SG;
> > > +
> > > +	sg_miter_start(&miter, sgl, nents, sg_flags);
> > > +
> > > +	while ((offset < buflen) && sg_miter_next(&miter)) {
> > > +		unsigned int len;
> > > +
> > > +		len = min(miter.length, buflen - offset);
> > > +
> > > +		/* When dram_access_quirk, the bounce buffer is a iomem mapping */
> > > +		if (host->dram_access_quirk) {
> > > +			if (to_buffer)
> > > +				memcpy_toio(buf + offset, miter.addr, len);
> > > +			else
> > > +				memcpy_fromio(miter.addr, buf + offset, len);
> > > +		} else {
> > > +			if (to_buffer)
> > > +				memcpy(buf + offset, miter.addr, len);
> > > +			else
> > > +				memcpy(miter.addr, buf + offset, len);
> > > +		}
> > > +
> > > +		offset += len;
> > > +	}
> > > +
> > > +	sg_miter_stop(&miter);
> > > +}
> > > +
> > >    static void meson_mmc_start_cmd(struct mmc_host *mmc, struct mmc_command *cmd)
> > >    {
> > >    	struct meson_host *host = mmc_priv(mmc);
> > > @@ -785,8 +827,7 @@ static void meson_mmc_start_cmd(struct mmc_host *mmc, struct mmc_command *cmd)
> > >    		if (data->flags & MMC_DATA_WRITE) {
> > >    			cmd_cfg |= CMD_CFG_DATA_WR;
> > >    			WARN_ON(xfer_bytes > host->bounce_buf_size);
> > > -			sg_copy_to_buffer(data->sg, data->sg_len,
> > > -					  host->bounce_buf, xfer_bytes);
> > > +			meson_mmc_copy_buffer(host, data, xfer_bytes, true);
> > >    			dma_wmb();
> > >    		}
> > >    
> > > @@ -955,8 +996,7 @@ static irqreturn_t meson_mmc_irq_thread(int irq, void *dev_id)
> > >    	if (meson_mmc_bounce_buf_read(data)) {
> > >    		xfer_bytes = data->blksz * data->blocks;
> > >    		WARN_ON(xfer_bytes > host->bounce_buf_size);
> > > -		sg_copy_from_buffer(data->sg, data->sg_len,
> > > -				    host->bounce_buf, xfer_bytes);
> > > +		meson_mmc_copy_buffer(host, data, xfer_bytes, false);
> > >    	}
> > >    
> > >    	next_cmd = meson_mmc_get_next_command(cmd);
> >
> > Best regards
>
>
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