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Date: Sat, 18 May 2024 08:01:14 +0100
From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Guenter Roeck <linux@roeck-us.net>
Cc: linux-arm-kernel@lists.infradead.org,
	Duanqiang Wen <duanqiangwen@net-swift.com>, mturquette@baylibre.com,
	sboyd@kernel.org, linux-clk@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] clkdev: report over-sized strings when creating clkdev
 entries
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Sender: Russell King (Oracle) <linux@armlinux.org.uk>

On Fri, May 17, 2024 at 08:24:19PM -0700, Guenter Roeck wrote:
> On 5/17/24 16:37, Russell King (Oracle) wrote:
> > On Fri, May 17, 2024 at 04:34:06PM -0700, Guenter Roeck wrote:
> > > On 5/17/24 15:22, Russell King (Oracle) wrote:
> > > > On Fri, May 17, 2024 at 03:09:12PM -0700, Guenter Roeck wrote:
> > > > > Hi,
> > > > > 
> > > > > On Fri, Mar 15, 2024 at 11:47:55AM +0000, Russell King (Oracle) wrote:
> > > > > > Report an error when an attempt to register a clkdev entry results in a
> > > > > > truncated string so the problem can be easily spotted.
> > > > > > 
> > > > > > Reported by: Duanqiang Wen <duanqiangwen@net-swift.com>
> > > > > > Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> > > > > > Reviewed-by: Stephen Boyd <sboyd@kernel.org>
> > > > > 
> > > > > With this patch in the mainline kernel, I get
> > > > > 
> > > > > 10000000.clock-controller:corepll: device ID is greater than 24
> > > > > sifive-clk-prci 10000000.clock-controller: Failed to register clkdev for corepll: -12
> > > > > sifive-clk-prci 10000000.clock-controller: could not register clocks: -12
> > > > > sifive-clk-prci 10000000.clock-controller: probe with driver sifive-clk-prci failed with error -12
> > > > > ...
> > > > > platform 10060000.gpio: deferred probe pending: platform: supplier 10000000.clock-controller not ready
> > > > > platform 10010000.serial: deferred probe pending: platform: supplier 10000000.clock-controller not ready
> > > > > platform 10011000.serial: deferred probe pending: platform: supplier 10000000.clock-controller not ready
> > > > > platform 10040000.spi: deferred probe pending: platform: supplier 10000000.clock-controller not ready
> > > > > platform 10050000.spi: deferred probe pending: platform: supplier 10000000.clock-controller not ready
> > > > > platform 10090000.ethernet: deferred probe pending: platform: supplier 10000000.clock-controller not ready
> > > > > 
> > > > > when trying to boot sifive_u in qemu.
> > > > > 
> > > > > Apparently, "10000000.clock-controller" is too long. Any suggestion on
> > > > > how to solve the problem ? I guess using dev_name(dev) as dev_id parameter
> > > > > for clk_hw_register_clkdev() is not or no longer a good idea.
> > > > > What else should be used instead ?
> > > > 
> > > > It was *never* a good idea. clkdev uses a fixed buffer size of 20
> > > > characters including the NUL character, and "10000000.clock-controller"
> > > > would have been silently truncated to "10000000.clock-cont", and thus
> > > > 
> > > >                           if (!dev_id || strcmp(p->dev_id, dev_id))
> > > > 
> > > > would never have matched.
> > > > 
> > > > We need to think about (a) whether your use of clk_hw_register_clkdev()
> > > > is still appropriate, and (b) whether we need to increase the size of
> > > > the strings.
> > > > 
> > > 
> > > It isn't _my_ use, really. I only run a variety of boot tests with qemu.
> > > I expect we'll see reports from others trying to boot the mainline kernel
> > > on real sifive_u hardware or other hardware using the same driver or other
> > > drivers using dev_name() as dev_id parameter. Coccinelle finds the
> > > following callers:
> > 
> > Using dev_name() is not an issue. It's when dev_name() exceeds 19
> > characters that it becomes an issue (and always has been an issue
> > due to the truncation.) clk_get(dev, ...) uses dev_name(dev) to match
> > against its entry in the table.
> > 
> > As I say, dev_name() itself is not an issue. The length used for the
> > name is.
> > 
> 
> Maybe, but the existence of best_dev_name() suggests that this has been seen
> before and that, as you mentioned, it is not a good idea. Anyway, the patch
> below fixes the problem for me. I don't know if it is acceptable / correct,
> so it might serve as guidance for others when fixing the problem for real.

I get the impression that there's a communication problem here, so I'm
not going to continue replying. Thanks.

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