From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from luna.linkmauve.fr (82-65-109-163.subs.proxad.net [82.65.109.163]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C3F913D5645; Thu, 16 Jul 2026 11:07:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=82.65.109.163 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784200054; cv=none; b=jZGYMYlgp2lS/6ZM0g+e8SU8yYkku6ugYXev8UAAXlXKB/g4bF2oAAzjH9umRYRrcocAgszQR2sKcHaIT24cEyX6dWSjYz9TxxnEjQM8GJcC9CSRBU12C03Zwaff2HLjUKGaXtPIdXUTiVDYAevd0aZF+MJbk49xUWeUFClCWh0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784200054; c=relaxed/simple; bh=Q6VGXW5tf9e1NERg0XxzMyBWsizwiO2Hrp5/U9CR138=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NabNtQBxbntOMOWeoMEQxWSNGGp8NSi8z0XgWpS78bvYv1D0vD330bfH4hCIsNfg4ybrFfdr1sTIalvv/sQk5DBd6AcSUk0A3GQHkCpNtulH+oe/k7CqAMiH5/eqFHv+xgyBOpw6AGiVyNvwRuURnLZctBjgsQcNI1ZpLdD0AIo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=linkmauve.fr; spf=pass smtp.mailfrom=linkmauve.fr; arc=none smtp.client-ip=82.65.109.163 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=linkmauve.fr Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linkmauve.fr Received: by luna.linkmauve.fr (Postfix, from userid 1000) id D604FF40D30; Thu, 16 Jul 2026 13:07:26 +0200 (CEST) Date: Thu, 16 Jul 2026 13:07:26 +0200 From: Link Mauve To: Andy Shevchenko Cc: Link Mauve , Srinivas Kandagatla , Andy Shevchenko , Sven Peter , Janne Grunau , Neal Gompa , Frank Li , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Vladimir Zapolskiy , =?iso-8859-1?Q?Andr=E9?= Draszik , Neil Armstrong , Kevin Hilman , Jerome Brunet , Martin Blumenstingl , Orson Zhai , Baolin Wang , Chunyan Zhang , Maxime Coquelin , Alexandre Torgue , Kalyani Akula , Michal Simek , Miguel Ojeda , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Danilo Krummrich , Daniel Almeida , Tamir Duberstein , Alexandre Courbot , Onur =?iso-8859-1?Q?=D6zkan?= , asahi@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, imx@lists.linux.dev, linux-amlogic@lists.infradead.org, linux-arm-msm@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, rust-for-linux@vger.kernel.org Subject: Re: [PATCH v2 0/2] nvmem: fix a const-unsoundness in reg_write Message-ID: References: <20260715195520.25410-1-linkmauve@linkmauve.fr> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="siXK+shzjeD2fFGh" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Jabber-ID: linkmauve@linkmauve.fr --siXK+shzjeD2fFGh Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit On Thu, Jul 16, 2026 at 12:03:17PM +0300, Andy Shevchenko wrote: > On Wed, Jul 15, 2026 at 09:55:16PM +0200, Link Mauve wrote: > > This callback used to take a mutable void * for no reason, which causes > > the compiler to be unaware that the val buffer should never be modified > > by the callback. > > > > This was found while drafting the nvmem-provider Rust abstraction. > > > > Thanks to the guidance of Andy Shevchenko, this now introduces a new > > callback and deprecates the existing one, with the goal of renaming the > > new one into the old one once no user remains in the kernel. > > You forgot to use --base. It's unclear against what should be this applied. > I tried Linux Next (next-20260715), and it fails. > > Yes, it applies against v7.2-rc3, but it means that this won't be applied on > top of maintainer's tree (which has something already that you have to take > into consideration). Indeed I developed against Linus’s master, I’ll rebase on linux-next for v3. > > For the record, the first version of the series was no go as the first patch > there breaks the things, like > > drivers/nvmem/qfprom.c:446:22: error: incompatible function pointer types assigning to 'nvmem_reg_write_t' (aka 'int (*)(void *, unsigned int, const void *, unsigned long)') from 'int (void *, unsigned int, void *, size_t)' (aka 'int (void *, unsigned int, void *, unsigned long)') [-Wincompatible-function-pointer-types] > 446 | econfig.reg_write = qfprom_reg_write; > | ^ ~~~~~~~~~~~~~~~~ > 1 error generated. > > This version doesn't have this issue (at least with my smoke build tests > on x86_64). Yup, I enabled the drivers but didn’t select COMPILE_TEST, so they didn’t actually build and I assumed everything was correct… This won’t happen again. > > Now, what catches me is that regmap_bulk_read() proto used for both cases in > drivers/nvmem/apple-spmi-nvmem.c without any changes. Which makes me think > that the approach can be done in a simpler way, id est converting users first > to use const specifiers in their callbacks first. But this trick is done with > using (void *) casting (?) which makes warning to disappear, which is > interesting case. So I think the Apple driver should actually use proper > protos and hence wrappers, otherwise it makes compiler blind, which is not > good. TL;DR: you should fix the Apple driver (and might more if any of them > use that dirty trick). This series only affects the reg_write callback, not reg_read, so it’s to be expected that regmap_bulk_read() keeps its void * parameter as it will modify it, it’s regmap_bulk_write() which correctly takes const void *. The Apple driver completely removes all function pointer safety by casting the function into void *, although that’s not due to const incompatibility but due to the first argument being struct regmap * instead of void *. I’ve attached a patch fixing this particular issue, I will include it in my v3 if that’s ok with you (or it could go as a different series, I don’t care much). I think I’ve found another bug in that driver, it says .max_register = 0xffff but .size = 0xffff, one or the other is probably off-by-one, and I suspect .size should be 0x10000 instead. > > -- > With Best Regards, > Andy Shevchenko > > Thanks! -- Link Mauve --siXK+shzjeD2fFGh Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename=0001-nvmem-apple-spmi-improve-calling-safety-with-wrapper.patch >From ec85ce97c6c835d99aa28b11b78af2744b45dc49 Mon Sep 17 00:00:00 2001 From: Link Mauve Date: Thu, 16 Jul 2026 12:59:13 +0200 Subject: [PATCH] nvmem: apple-spmi: improve calling safety with wrapper functions This driver used to cast the regmap_bulk_*() functions to void *, bypassing any compiler safety around incompatible function pointers. With two small helpers, which just convert the void * priv parameter into the wanted struct regmap *, we can remove the void * cast altogether. Signed-off-by: Link Mauve --- drivers/nvmem/apple-spmi-nvmem.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/drivers/nvmem/apple-spmi-nvmem.c b/drivers/nvmem/apple-spmi-nvmem.c index cbf25c53d048..81d9e242c836 100644 --- a/drivers/nvmem/apple-spmi-nvmem.c +++ b/drivers/nvmem/apple-spmi-nvmem.c @@ -18,6 +18,20 @@ static const struct regmap_config apple_spmi_regmap_config = { .max_register = 0xffff, }; +static int apple_spmi_nvmem_read(void *priv, unsigned int offset, + void *val, size_t bytes) +{ + struct regmap *regmap = priv; + return regmap_bulk_read(regmap, offset, val, bytes); +} + +static int apple_spmi_nvmem_write(void *priv, unsigned int offset, + const void *val, size_t bytes) +{ + struct regmap *regmap = priv; + return regmap_bulk_write(regmap, offset, val, bytes); +} + static int apple_spmi_nvmem_probe(struct spmi_device *sdev) { struct regmap *regmap; @@ -28,8 +42,8 @@ static int apple_spmi_nvmem_probe(struct spmi_device *sdev) .word_size = 1, .stride = 1, .size = 0xffff, - .reg_read = (void *)regmap_bulk_read, - .reg_write_const = (void *)regmap_bulk_write, + .reg_read = apple_spmi_nvmem_read, + .reg_write_const = apple_spmi_nvmem_write, }; regmap = devm_regmap_init_spmi_ext(sdev, &apple_spmi_regmap_config); -- 2.55.0 --siXK+shzjeD2fFGh--