linux-kernel - Re: [PATCH] clk: vc5: Avoid divide by zero when rounding or setting rates

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Message-ID: <153324317799.10763.16530922080427544645@swboyd.mtv.corp.google.com>
Date:   Thu, 02 Aug 2018 13:52:57 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Marek Vasut <marek.vasut@...il.com>,
        Michael Turquette <mturquette@...libre.com>,
        Steve Longerbeam <slongerbeam@...il.com>
Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH] clk: vc5: Avoid divide by zero when rounding or setting rates

Quoting Steve Longerbeam (2018-07-18 10:56:51)
> 
> 
> On 07/06/2018 11:23 AM, Stephen Boyd wrote:
> > Quoting Steve Longerbeam (2018-05-31 18:59:17)
> >> Add checks in the .round_rate and .set_rate ops for zero requested
> >> rate or zero parent rate. If either are zero in .round_rate, just
> >> return zero. If either are zero in .set_rate, return -EINVAL.
> > Are you seeing problems when the clk is unparented and we're trying to
> > recalculate the rate or change rates, and thus the parent frequency
> > looks like 0?
> 
> The problem appeared when suspending the rcar-du driver.
> The kernel tested is a Renesas BSP release (3.6.2), and in the
> version of the rcar-du driver from that release, the driver calls
> clk_set_rate() with a rate of zero in its suspend PM op. This is
> fixed in mainline kernel. So the divide-by-zero in vc5 clock driver
> probably will not show up in mainline.

Ok so then this patch shouldn't be applied on mainline?

> 
> >   Should this get a Fixes: tag so that it goes back to
> > stable kernels?
> >
> 
> Zero rates are not checked beginning with the initial commit
> 3e1aec4e2c ("clk: vc5: Add support for IDT VersaClock 5P49V5923 and 
> 5P49V5933").
> so that would have to be the Fixes: tag.

Thanks!