From: Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
To: Michal Nazarewicz <mpn-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
Cc: Laxman Dewangan
<ldewangan-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>,
Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH] spi: tegra: avoid unsigned->signed->unsigned promotion
Date: Fri, 29 Nov 2013 22:43:15 +0100 [thread overview]
Message-ID: <20131129214313.GA18036@mithrandir> (raw)
In-Reply-To: <1385745164-10534-1-git-send-email-mpn-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
[-- Attachment #1: Type: text/plain, Size: 1041 bytes --]
On Fri, Nov 29, 2013 at 06:12:44PM +0100, Michal Nazarewicz wrote:
> From: Michal Nazarewicz <mina86-deATy8a+UHjQT0dZR+AlfA@public.gmane.org>
>
> u8 type, which is unsigned, is promoted to int, which is singned, when
> doing a binary shift. Then, on 64-bit machines, it is further promoted
> to unsigned long which may lead to more significant half of the value
> to be all ones. To avoid this, explicitly promote to an unsigned type.
So this would only become an problem on 64-bit Tegra SoCs, right? I
suspect that there are quite a few places where something similar is
done and which suffer from the same issue.
But I don't think there's a real issue here. Even on 64-bit platforms,
writel() will only write 32-bit registers, and therefore discard the
upper 32 bits.
I think in general perhaps a more proper fix would be to use only u32
instead of unsigned long for these cases, since then the problem goes
away. u32 is also the type of the value used by writel() so it makes
perfect sense to use it.
Thierry
[-- Attachment #2: Type: application/pgp-signature, Size: 836 bytes --]
next prev parent reply other threads:[~2013-11-29 21:43 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-29 17:12 [PATCH] spi: tegra: avoid unsigned->signed->unsigned promotion Michal Nazarewicz
[not found] ` <1385745164-10534-1-git-send-email-mpn-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2013-11-29 21:43 ` Thierry Reding [this message]
2013-12-02 13:05 ` Michal Nazarewicz
2013-12-08 15:35 ` [PATCH 0/3] spi: tegra: use u32 for 32-bit register values Michal Nazarewicz
[not found] ` <1386516911-26388-1-git-send-email-mina86-deATy8a+UHjQT0dZR+AlfA@public.gmane.org>
2013-12-08 15:35 ` [PATCH 1/3] spi: tegra114: " Michal Nazarewicz
2013-12-08 15:35 ` [PATCH 2/3] spi: tegra20-slink: " Michal Nazarewicz
2013-12-08 15:35 ` [PATCH 3/3] spi: tegra20-sflash: " Michal Nazarewicz
2013-12-09 18:00 ` [PATCH 0/3] spi: tegra: " Stephen Warren
2013-12-09 18:14 ` Mark Brown
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20131129214313.GA18036@mithrandir \
--to=thierry.reding-re5jqeeqqe8avxtiumwx3w@public.gmane.org \
--cc=broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org \
--cc=ldewangan-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org \
--cc=linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
--cc=linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
--cc=linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
--cc=mpn-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).