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

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Message-ID: <a88e1546-1530-4326-b0ee-dc4e50d0343f@csgroup.eu>
Date: Sat, 8 Nov 2025 12:14:50 +0100
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: "Sverdlin, Alexander" <alexander.sverdlin@...mens.com>,
 "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Cc: "hui.wang@...onical.com" <hui.wang@...onical.com>,
 "mwalle@...nel.org" <mwalle@...nel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "florent.trinh-thai@...soprasteria.com"
 <florent.trinh-thai@...soprasteria.com>, "arnd@...db.de" <arnd@...db.de>
Subject: Re: [PATCH] eeprom: at25: convert to spi-mem API

Hi Again,

Le 08/11/2025 à 11:05, Christophe Leroy a écrit :
> Hi Alexander,
> 
> 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 ?

Christophe