can: etas_es58x: rework the version check logic to silence -Wformat-truncation

Following [1], es58x_devlink.c now triggers the following
format-truncation GCC warnings:

drivers/net/can/usb/etas_es58x/es58x_devlink.c: In function ‘es58x_devlink_info_get’:
drivers/net/can/usb/etas_es58x/es58x_devlink.c:201:41: warning: ‘%02u’ directive output may be truncated writing between 2 and 3 bytes into a region of size between 1 and 3 [-Wformat-truncation=]
201 | snprintf(buf, sizeof(buf), "%02u.%02u.%02u",
| ^~~~
drivers/net/can/usb/etas_es58x/es58x_devlink.c:201:30: note: directive argument in the range [0, 255]
201 | snprintf(buf, sizeof(buf), "%02u.%02u.%02u",
| ^~~~~~~~~~~~~~~~
drivers/net/can/usb/etas_es58x/es58x_devlink.c:201:3: note: ‘snprintf’ output between 9 and 12 bytes into a destination of size 9
201 | snprintf(buf, sizeof(buf), "%02u.%02u.%02u",
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
202 | fw_ver->major, fw_ver->minor, fw_ver->revision);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/can/usb/etas_es58x/es58x_devlink.c:211:41: warning: ‘%02u’ directive output may be truncated writing between 2 and 3 bytes into a region of size between 1 and 3 [-Wformat-truncation=]
211 | snprintf(buf, sizeof(buf), "%02u.%02u.%02u",
| ^~~~
drivers/net/can/usb/etas_es58x/es58x_devlink.c:211:30: note: directive argument in the range [0, 255]
211 | snprintf(buf, sizeof(buf), "%02u.%02u.%02u",
| ^~~~~~~~~~~~~~~~
drivers/net/can/usb/etas_es58x/es58x_devlink.c:211:3: note: ‘snprintf’ output between 9 and 12 bytes into a destination of size 9
211 | snprintf(buf, sizeof(buf), "%02u.%02u.%02u",
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
212 | bl_ver->major, bl_ver->minor, bl_ver->revision);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/can/usb/etas_es58x/es58x_devlink.c:221:38: warning: ‘%03u’ directive output may be truncated writing between 3 and 5 bytes into a region of size between 2 and 4 [-Wformat-truncation=]
221 | snprintf(buf, sizeof(buf), "%c%03u/%03u",
| ^~~~
drivers/net/can/usb/etas_es58x/es58x_devlink.c:221:30: note: directive argument in the range [0, 65535]
221 | snprintf(buf, sizeof(buf), "%c%03u/%03u",
| ^~~~~~~~~~~~~
drivers/net/can/usb/etas_es58x/es58x_devlink.c:221:3: note: ‘snprintf’ output between 9 and 13 bytes into a destination of size 9
221 | snprintf(buf, sizeof(buf), "%c%03u/%03u",
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
222 | hw_rev->letter, hw_rev->major, hw_rev->minor);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This is not an actual bug because the sscanf() parsing makes sure that
the u8 are only two digits long and the u16 only three digits long.
Thus below declaration:

char buf[max(sizeof("xx.xx.xx"), sizeof("axxx/xxx"))];

allocates just what is needed to represent either of the versions.

This warning was known but ignored because, at the time of writing,
-Wformat-truncation was not present in the kernel, not even at W=3 [2].

One way to silence this warning is to check the range of all sub
version numbers are valid: [0, 99] for u8 and range [0, 999] for u16.

The module already has a logic which considers that when all the sub
version numbers are zero, the version number is not set. Note that not
having access to the device specification, this was an arbitrary
decision. This logic can thus be removed in favor of global check that
would cover both cases:

- the version number is not set (parsing failed)
- the version number is not valid (paranoiac check to please gcc)

Before starting to parse the product info string, set the version
sub-numbers to the maximum unsigned integer thus violating the
definitions of struct es58x_sw_version or struct es58x_hw_revision.

Then, rework the es58x_sw_version_is_set() and
es58x_hw_revision_is_set() functions: remove the check that the
sub-numbers are non zero and replace it by a check that they fit in
the expected number of digits. This done, rename the functions to
reflect the change and rewrite the documentation. While doing so, also
add a description of the return value.

Finally, the previous version only checked that
&es58x_hw_revision.letter was not the null character. Replace this
check by an alphanumeric character check to make sure that we never
return a special character or a non-printable one and update the
documentation of struct es58x_hw_revision accordingly.

All those extra checks are paranoid but have the merit to silence the
newly introduced W=1 format-truncation warning [1].

[1] commit 6d4ab2e97dcf ("extrawarn: enable format and stringop overflow warnings in W=1")
Link: https://git.kernel.org/torvalds/c/6d4ab2e97dcf

[2] https://lore.kernel.org/all/CAMZ6Rq+K+6gbaZ35SOJcR9qQaTJ7KR0jW=XoDKFkobjhj8CHhw@mail.gmail.com/

Reported-by: Marc Kleine-Budde <mkl@pengutronix.de>
Closes: https://lore.kernel.org/linux-can/20230914-carrousel-wrecker-720a08e173e9-mkl@pengutronix.de/
Fixes: 9f06631c3f1f ("can: etas_es58x: export product information through devlink_ops::info_get()")
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/all/20230924110914.183898-2-mailhol.vincent@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

can: etas_es58x: export product information through devlink_ops::info_get()

ES58x devices report below product information through a custom usb
string:

* the firmware version
* the bootloader version
* the hardware revision

Parse this string, store the results in struct es58x_dev, export:

* the firmware version through devlink's "fw" name
* the bootloader version through devlink's "fw.bootloader" name
* the hardware revisionthrough devlink's "board.rev" name

Those devlink entries are not critical to use the device, if parsing
fails, print an informative log message and continue to probe the
device.

In addition to that, use usb_device::serial to report the device
serial number.

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/all/20221130174658.29282-6-mailhol.vincent@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

can: etas_es58x: add devlink support

Add basic support for devlink at the device level. The callbacks of
struct devlink_ops will be implemented next.

Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/all/20221130174658.29282-2-mailhol.vincent@wanadoo.fr
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>