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? -Doug
