Re: [PATCH] clkdev: report over-sized strings when creating clkdev entries

["Russell King (Oracle)" <linux@armlinux.org.uk>]

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.

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