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Date: Wed, 16 Jan 2019 17:31:12 -0500
From: Sebastien Bourdelin <sebastien.bourdelin@...il.com>
To: Himanshu Jha <himanshujha199640@...il.com>
Cc: linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
linux-iio@...r.kernel.org, mark.rutland@....com,
robh+dt@...nel.org, pmeerw@...erw.net, lars@...afoo.de,
knaack.h@....de, jic23@...nel.org
Subject: Re: [PATCH v2 1/2] iio: chemical: bme680: Add device-tree support
Hi Himanshu,
On 1/15/19 1:41 PM, Himanshu Jha wrote:
> ...
> himanshu@...anshu-Vostro-3559:~/linux-next$ sudo make drivers/iio/chemical/bme680_spi.o
> scripts/kconfig/conf --syncconfig Kconfig
> make[1]: Nothing to be done for 'all'.
> HOSTCC scripts/dtc/dtc.o
> HOSTCC scripts/dtc/flattree.o
> HOSTCC scripts/dtc/fstree.o
> HOSTCC scripts/dtc/data.o
> HOSTCC scripts/dtc/livetree.o
> HOSTCC scripts/dtc/treesource.o
> HOSTCC scripts/dtc/srcpos.o
> HOSTCC scripts/dtc/checks.o
> HOSTCC scripts/dtc/util.o
> LEX scripts/dtc/dtc-lexer.lex.c
> YACC scripts/dtc/dtc-parser.tab.h
> HOSTCC scripts/dtc/dtc-lexer.lex.o
> YACC scripts/dtc/dtc-parser.tab.c
> HOSTCC scripts/dtc/dtc-parser.tab.o
> HOSTLD scripts/dtc/dtc
> CC scripts/mod/empty.o
> MKELF scripts/mod/elfconfig.h
> HOSTCC scripts/mod/modpost.o
> CC scripts/mod/devicetable-offsets.s
> HOSTCC scripts/mod/file2alias.o
> HOSTCC scripts/mod/sumversion.o
> HOSTLD scripts/mod/modpost
> CC kernel/bounds.s
> CC arch/x86/kernel/asm-offsets.s
> CALL scripts/checksyscalls.sh
> DESCEND objtool
> CC drivers/iio/chemical/bme680_spi.o
>
> Compiles without any issues.
>> Hum, weird it compiles actually :s
> I think this behavior is observed due to:
>
> include/linux/module.h +212
>
> #ifdef MODULE
> /* Creates an alias so file2alias.c can find device table. */
> #define MODULE_DEVICE_TABLE(type, name) \
> extern typeof(name) __mod_##type##__##name##_device_table \
> __attribute__ ((unused, alias(__stringify(name))))
> #else /* !MODULE */
> #define MODULE_DEVICE_TABLE(type, name)
> #endif
>
> So, when we build the driver as a module[M] then macro expansion
> takes place giving us the compiler warning.
>
> OTOH, if the driver is built as builtin[*] then marco expands
> to nothing or simply goes away. And `;' completes the struct
> declaration while silencing the warning.
>
> static const struct of_device_id bme680_of_spi_match[] = {
> { .compatible = "bosch,bme680", },
> {},
> }
> MODULE_DEVICE_TABLE(of, bme680_of_spi_match);
>
> converts to:
>
> static const struct of_device_id bme680_of_spi_match[] = {
> { .compatible = "bosch,bme680", },
> {},
> }
> ;
> ^^^
>
> Amazing!
> Correct me if I'm wrong somewhere, took me 2 hours to figure
> that out :D
Ahah, nice!
Thanks a lot for the explanation!
> Also, I some additional interesting observations:
>
> When buitin[*] -> no symbol tables in the RO segment of object file
>
> himanshu@...anshu-Vostro-3559:~/linux-next$ nm drivers/iio/chemical/bme680_spi.o
> 0000000000000000 d __addressable_bme680_spi_driver_init130
> 00000000000001a0 r bme680_acpi_match
> U bme680_core_probe
> 0000000000000000 r bme680_of_spi_match
> 00000000000000a0 d bme680_regmap_bus
> U bme680_regmap_config
> 0000000000000000 t bme680_regmap_spi_read
> 0000000000000010 t bme680_regmap_spi_write
> 0000000000000000 d bme680_spi_driver
> 0000000000000000 t bme680_spi_driver_exit
> 0000000000000000 t bme680_spi_driver_init
> 00000000000001e0 r bme680_spi_id
> 0000000000000070 t bme680_spi_probe
> U _dev_err
> U __devm_regmap_init
> U driver_unregister
> 0000000000000000 d __exitcall_bme680_spi_driver_exit
> 0000000000000000 t __initcall_bme680_spi_driver_init6
> U regmap_read
> U regmap_update_bits_base
> U regmap_write
> U spi_get_device_id
> U __spi_register_driver
> U spi_setup
> U spi_write_then_read
> U __stack_chk_fail
>
>
> While when [M] -> we can see the symbol tables in the RO segment
>
> himanshu@...anshu-Vostro-3559:~/linux-next$ nm drivers/iio/chemical/bme680_spi.o
> 00000000000001a0 r bme680_acpi_match
> U bme680_core_probe
> 0000000000000000 r bme680_of_spi_match
> 00000000000000a0 d bme680_regmap_bus
> U bme680_regmap_config
> 0000000000000000 t bme680_regmap_spi_read
> 0000000000000010 t bme680_regmap_spi_write
> 0000000000000000 d bme680_spi_driver
> 0000000000000000 t bme680_spi_driver_exit
> 0000000000000000 t bme680_spi_driver_init
> 00000000000001e0 r bme680_spi_id
> 0000000000000070 t bme680_spi_probe
> 0000000000000000 T cleanup_module
> U _dev_err
> U __devm_regmap_init
> U driver_unregister
> 0000000000000000 T init_module
> 00000000000001a0 R __mod_acpi__bme680_acpi_match_device_table <---
> 0000000000000000 R __mod_of__bme680_of_spi_match_device_table <---
> 00000000000001e0 R __mod_spi__bme680_spi_id_device_table <---
> U regmap_read
> U regmap_update_bits_base
> U regmap_write
> U spi_get_device_id
> U __spi_register_driver
> U spi_setup
> U spi_write_then_read
> U __stack_chk_fail
> U __this_module
> 0000000000000033 r __UNIQUE_ID_author38
> 000000000000000f r __UNIQUE_ID_description39
> 0000000000000000 r __UNIQUE_ID_license40
>
>
> Thanks!
Thanks to you :)
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