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Date:   Tue, 12 Dec 2023 15:03:02 -0500
From:   Hugo Villeneuve <hugo@hugovil.com>
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     kernel test robot <lkp@intel.com>, gregkh@linuxfoundation.org,
        jirislaby@kernel.org, hvilleneuve@dimonoff.com,
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Subject: Re: [PATCH 1/7] serial: sc16is7xx: fix snprintf format specifier in
 sc16is7xx_regmap_name()
Precedence: bulk

On Thu, 7 Dec 2023 20:24:45 +0200
Andy Shevchenko <andy.shevchenko@gmail.com> wrote:

> On Thu, Dec 7, 2023 at 7:52 PM Hugo Villeneuve <hugo@hugovil.com> wrote:
> > On Wed, 6 Dec 2023 14:29:39 +0800
> > kernel test robot <lkp@intel.com> wrote:
> 
> ...
> 
> > >    drivers/tty/serial/sc16is7xx.c: In function 'sc16is7xx_i2c_probe':
> > > >> drivers/tty/serial/sc16is7xx.c:1703:41: warning: '%u' directive output may be truncated writing between 1 and 10 bytes into a region of size 2 [-Wformat-truncation=]
> > >     1703 |         snprintf(buf, sizeof(buf), "port%u", port_id);
> > >          |                                         ^~
> > >    In function 'sc16is7xx_regmap_name',
> > >        inlined from 'sc16is7xx_i2c_probe' at drivers/tty/serial/sc16is7xx.c:1805:17:
> > >    drivers/tty/serial/sc16is7xx.c:1703:36: note: directive argument in the range [0, 4294967294]
> > >     1703 |         snprintf(buf, sizeof(buf), "port%u", port_id);
> > >          |                                    ^~~~~~~~
> > >    drivers/tty/serial/sc16is7xx.c:1703:9: note: 'snprintf' output between 6 and 15 bytes into a destination of size 6
> > >     1703 |         snprintf(buf, sizeof(buf), "port%u", port_id);
> > >          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> > Hi,
> > the only solution I could find is to add this line just before snprintf:
> >
> >     BUG_ON(port_id > MAX310X_MAX_PORTS);
> >
> > it allows us to have the smallest buffer size possible.
> >
> > One other solution would be to change port_id from "unsigned int"
> > to "u8", and increase the buffer by an additional 2 bytes to silence
> > the warning, but then wasting 2 bytes for each channel, like so:
> 
> I didn't get this. It's a buffer that is rewritten on each port (why
> is it even static?). Just make sure it's enough for any given number
> and drop the static.
> 
> ...
> 
> While at it, can you look at the following items to improve?
> - sc16is7xx_alloc_line() can be updated to use IDA framework
> - move return xxx; to the default cases in a few functions
> - if (div > 0xffff) { --> if (div >= BIT(16)) { as it better shows why
> the limit is that (we have only 16 bits for the divider)
> - do {} while (0) in the sc16is7xx_port_irq, WTH?!
> - while (1) { -- do { } while (keep_polling); in sc16is7xx_irq()
> - use in_range() in sc16is7xx_setup_mctrl_ports() ? (maybe not, dunno)
> - for (i--; i >= 0; i--) { --> while (i--) {
> - use spi_get_device_match_data() and i2c_get_match_data()
> - 15000000 --> 15 * HZ_PER_MHZ ?
> - dropping MODULE_ALIAS (and fix the ID tables, _if_ needed)
> - split the code to the core / main + SPI + I2C glue drivers
> 
> * These just come on the first glance at the code, perhaps there is
> more room to improve.

Hi Andy,
just to let you know that I have implemented almost all of the fixes /
improvements. I will submit them once V2 of this current series
lands in Greg's next tree.

However, for sc16is7xx_alloc_line(), I looked at using the IDA framework
but it doesn't seem possible because there is no IDA function
to search if a bit is set, which is a needed functionality.

Hugo Villeneuve