On Wed, Feb 7, 2024 at 3:00 PM Srinivas Kandagatla
<srinivas.kandagatla@xxxxxxxxxx> wrote:
>
>
>
> On 07/02/2024 06:35, Joy Chakraborty wrote:
> > On Wed, Feb 7, 2024 at 4:06 AM Srinivas Kandagatla
> > <srinivas.kandagatla@xxxxxxxxxx> wrote:
> >>
> >>
> >>
> >> On 06/02/2024 04:24, Joy Chakraborty wrote:
> >>> reg_read() callback registered with nvmem core expects an integer error
> >>> as a return value but rmem_read() returns the number of bytes read, as a
> >>> result error checks in nvmem core fail even when they shouldn't.
> >>>
> >>> Return 0 on success where number of bytes read match the number of bytes
> >>> requested and a negative error -EINVAL on all other cases.
> >>>
> >>> Fixes: 5a3fa75a4d9c ("nvmem: Add driver to expose reserved memory as nvmem")
> >>> Cc: stable@xxxxxxxxxxxxxxx
> >>> Signed-off-by: Joy Chakraborty <joychakr@xxxxxxxxxx>
> >>> ---
> >>> drivers/nvmem/rmem.c | 7 ++++++-
> >>> 1 file changed, 6 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/nvmem/rmem.c b/drivers/nvmem/rmem.c
> >>> index 752d0bf4445e..a74dfa279ff4 100644
> >>> --- a/drivers/nvmem/rmem.c
> >>> +++ b/drivers/nvmem/rmem.c
> >>> @@ -46,7 +46,12 @@ static int rmem_read(void *context, unsigned int offset,
> >>>
> >>> memunmap(addr);
> >>>
> >>> - return count;
> >>> + if (count != bytes) {
> >>
> >> How can this fail unless the values set in priv->mem->size is incorrect
> >>
> >
> > That should be correct since it would be fetched from the reserved
> > memory definition in the device tree.
> >
> >> Only case I see this failing with short reads is when offset cross the
> >> boundary of priv->mem->size.
> >>
> >>
> >> can you provide more details on the failure usecase, may be with actual
> >> values of offsets, bytes and priv->mem->size?
> >>
> >
> > This could very well happen if a fixed-layout defined for the reserved
> > memory has a cell which defines an offset and size greater than the
> > actual size of the reserved mem.
>
> No that should just be blocked from core layer, atleast which is what is
> checked bin_attr_nvmem_read(), if checks are missing in other places
> then that needs fixing.
>
Sure.
>
> > For E.g. if the device tree node is as follows
> > reserved-memory {
> > #address-cells = <1>;
> > #size-cells = <1>;
> > ranges;
> > nvmem@1000 {
> > compatible = "nvmem-rmem";
> > reg = <0x1000 0x400>;
> > no-map;
> > nvmem-layout {
> > compatible = "fixed-layout";
> > #address-cells = <1>;
> > #size-cells = <1>;
> > calibration@13ff {
> > reg = <0x13ff 0x2>;
>
> this is out of range, core should just err out.
>
Cells are currently unchecked, I can fix that in a different patch.
> --srini
>
> > };
> > };
> > };
> > };
> > If we try to read the cell "calibration" which crosses the boundary of
> > the reserved memory then it will lead to a short read.
> > Though, one might argue that the protection against such cell
> > definition should be there during fixed-layout parsing in core itself
> > but that is not there now and would not be a fix.
> >
> > What I am trying to fix here is not exactly short reads but how the
> > return value of rmem_read() is treated by the nvmem core, where it
> > treats a non-zero return from read as an error currently. Hence
> > returning the number of bytes read leads to false failures if we try
> > to read a cell.
> >
> >
> >>
> >>> + dev_err(priv->dev, "Failed read memory (%d)\n", count);
> >>> + return -EINVAL;
> >>> + }
> >>> +
> >>
> >>> + return 0;
> >>
> >> thanks,
> >> srini
> >>
> >>> }
> >>>
> >>> static int rmem_probe(struct platform_device *pdev)
Thanks
Joy
