Re: [PATCH 1/3] nvmem: core: Add functions to make number reading easy

[Srinivas Kandagatla]

On 10/03/2021 15:50, Doug Anderson wrote:
> Hi,
>
> On Wed, Mar 10, 2021 at 2:37 AM Srinivas Kandagatla
> <srinivas.kandagatla@xxxxxxxxxx> wrote:
> > On 06/03/2021 00:26, Douglas Anderson wrote:
> > > Sometimes the clients of nvmem just want to get a number out of
> > > nvmem. They don't want to think about exactly how many bytes the nvmem
> > > cell took up. They just want the number. Let's make it easy.
> > >
> > > In general this concept is useful because nvmem space is precious and
> > > usually the fewest bits are allocated that will hold a given value on
> > > a given system. However, even though small numbers might be fine on
> > > one system that doesn't mean that logically the number couldn't be
> > > bigger. Imagine nvmem containing a max frequency for a component. On
> > > one system perhaps that fits in 16 bits. On another system it might
> > > fit in 32 bits. The code reading this number doesn't care--it just
> > > wants the number.
> > >
> > > We'll provide two functions: nvmem_cell_read_variable_le_u32() and
> > > nvmem_cell_read_variable_le_u64().
> > >
> > > Comparing these to the existing functions like nvmem_cell_read_u32():
> > > * These new functions have no problems if the value was stored in
> > >     nvmem in fewer bytes. It's OK to use these function as long as the
> > >     value stored will fit in 32-bits (or 64-bits).
> > > * These functions avoid problems that the earlier APIs had with bit
> > >     offsets. For instance, you can't use nvmem_cell_read_u32() to read a
> > >     value has nbits=32 and bit_offset=4 because the nvmem cell must be
> > >     at least 5 bytes big to hold this value. The new API accounts for
> > >     this and works fine.
> > > * These functions make it very explicit that they assume that the
> > >     number was stored in little endian format. The old functions made
> > >     this assumption whenever bit_offset was non-zero (see
> > >     nvmem_shift_read_buffer_in_place()) but didn't whenever the
> > >     bit_offset was zero.
> > >
> > > NOTE: it's assumed that we don't need an 8-bit or 16-bit version of
> > > this function. The 32-bit version of the function can be used to read
> > > 8-bit or 16-bit data.
> > >
> > > At the moment, I'm only adding the "unsigned" versions of these
> > > functions, but if it ends up being useful someone could add a "signed"
> > > version that did 2's complement sign extension.
> > >
> > > At the moment, I'm only adding the "little endian" versions of these
> > > functions. Adding the "big endian" version would require adding "big
> > > endian" support to nvmem_shift_read_buffer_in_place().
> > >
> > > Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> > > ---
> > > This is a logical follow-up to:
> > >     https://lore.kernel.org/r/20210227002603.3260599-1-dianders@xxxxxxxxxxxx/
> > > ...but since it doesn't really share any of the same patches I'm not
> > > marking it as a v2.
> > >
> > >    drivers/nvmem/core.c           | 95 ++++++++++++++++++++++++++++++++++
> > >    include/linux/nvmem-consumer.h |  4 ++
> > >    2 files changed, 99 insertions(+)
> >
> > This patch as it is LGTM.
> >
> > If you plan to take this via other trees, here is
> >
> > Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
>
> Thanks! I think none of this is terribly urgent, though. Unless
> someone has a different opinion, my thought would be:
>
> * This patch lands in your tree for 5.13.
>
> * I'll snooze the email for 2 months and poke patch #2 and #3 once
> 5.13-rc1 is out.
>
> Does that sound OK to you?
That works for me!

Applied thanks!

--srini
> -Doug