Re: [PATCH V2 5/5] remoteproc: imx_rproc: change to ioremap_wc for dram

[Dong Aisheng <dongas86@gmail.com>]

On Wed, Jul 14, 2021 at 1:06 AM Mathieu Poirier
<mathieu.poirier@linaro.org> wrote:
>
> On Wed, Jul 07, 2021 at 05:40:33PM +0800, Dong Aisheng wrote:
> > DRAM is not io memory, so changed to ioremap_wc. This is also
> > aligned with core io accessories. e.g. memcpy/memset and cpu direct
> > access.
> >
> > Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
> > Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Fixes: 5e4c1243071d ("remoteproc: imx_rproc: support remote cores booted before Linux Kernel")
> > Reviewed-by: Peng Fan <peng.fan@nxp.com>
> > Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
> > ---
> > v1->v2:
> >  * new patch
>
> It's a new patch and yet Peng's RB tag is already on it...
>
> > ---
> >  drivers/remoteproc/imx_rproc.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/remoteproc/imx_rproc.c b/drivers/remoteproc/imx_rproc.c
> > index ff620688fad9..4ae416ba5080 100644
> > --- a/drivers/remoteproc/imx_rproc.c
> > +++ b/drivers/remoteproc/imx_rproc.c
> > @@ -597,7 +597,7 @@ static int imx_rproc_addr_init(struct imx_rproc *priv,
> >                       break;
> >
> >               /* Not use resource version, because we might share region */
> > -             priv->mem[b].cpu_addr = devm_ioremap(&pdev->dev, res.start, resource_size(&res));
> > +             priv->mem[b].cpu_addr = devm_ioremap_wc(&pdev->dev, res.start, resource_size(&res));
>
> How was it working before?  Will it really work for all platforms and was this
> extensively tested?

Here it is only used for accessing resource tables in DRAM which is
published by M core.

Why it works before is because:
1. the default memory access in remoteproc core (.e.g memcpy or direct
access by pointer
by CPU) seems also work well even it's device memory type mapped by
devm_ioremap.
e.g. cpu direct access
offset = rproc->table_ptr->offset[i]

2.  It will not work with meset() in rproc_elf_load_segments() which
has cache operations internally.
e.g. arch/arm64/lib/memset.S
However, it's lucky that for IMX cases, the resource table in DRAM are
currently used by early boot
(e.g. uboot/scfw loading M4 firmware), no chance to run into
rproc_elf_load_segments(),
so no issues so far.

Then the question is should we change the mapping type of resource
table mem to normal
memory (ioremap_wc) as remoteproc core are using normal memory accessories?

I guess we should do that, that's how this patch comes out.

Regards
Aisheng

>
> Peng - I will need an explicit reply from you that you are in agreement with
> this change.  I will also need you to review patch 01 and 02 of this set.
>
> Thanks,
> Mathieu
>
> >               if (!priv->mem[b].cpu_addr) {
> >                       dev_err(dev, "failed to remap %pr\n", &res);
> >                       return -ENOMEM;
> > --
> > 2.25.1
> >

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