Re: [PATCH] eeprom: at25: convert to spi-mem API

["Sverdlin, Alexander" <alexander.sverdlin@siemens.com>]

Hi Christophe,

On Sat, 2025-11-08 at 12:14 +0100, Christophe Leroy wrote:
> > Now I'm trying to understand why the problem surfaced with commit 
> > 8ad6249c51d0 ("eeprom: at25: convert to spi-mem API")
> > 
> 
> The reason why it was not a problem before was that the transfer was 
> done into of->prealloc_buf (fs/kernfs/file.c) which is a kmalloc() with 
> size (PAGE_SIZE + 1).
> 
> Following the rework of at25 it now goes into the bounce buffer which is 
> allocated with the exact size of the transfer.
> 
> Why do we need an intermediate bounce buffer now, why can't 
> of->prealloc_buf be used directly as before ?

userspace access is only one part of the story, the other is NVMEM
kernel-internal API, like nvmem_cell_read*() and I suppose there is
no requirement for a destination buffer to be DMA-able.

-- 
Alexander Sverdlin
Siemens AG
www.siemens.com