Hi Nicolas, (adding the linux-gpio mailing-list and Linus W.) On 03/10/2015 02:53 AM, Nicolas Schichan wrote:
Hello Alexandre, Using the latest 3.19 kernel, the bcm63xx GPIO code under arch/mips/bcm63xx/gpio.c is unable to register the gpio chip via gpiochip_add(), as it returns -ENOMEM. The kcalloc call for the gpio_desc array fails, as during prom code, it is too early for the kmalloc to work. It looks like the issue is caused by your patch: "gpio: remove gpio_descs global array"
Indeed. This happens because we removed the global GPIO array and replaced it with a more flexible per-chip array of GPIOs. We were hoping that issues like this one would have been caught in -next, but sadly the problem with bcm63xx went unnoticed until now. :(
Could you please advise on how to fix/workaround that ? (ideally while keeping the possibility to invoke the gpiolib code from the setup/prom code).
The only allocation performed by gpiochip_add() is the array of gpio_descs. Having this array pre-allocated in your early code (maybe by using a static array variable) and passing it to a gpiochip_add_early() function would do the trick.
However, it is not that simple since gpio_desc is a private structure which details (including its size) are not visible outside of drivers/gpio.
Another solution I could see would be to have a kernel config option that would make gpiolib "pre-allocate" a number of gpio descriptors as a static array for such cases - similar to the global GPIO array, but not as big.
Finally, we can also restore the global GPIO array as a config option for the few architectures that need it.
Of course, I would prefer a solution based on dynamic allocation - is there a kind a primitive memory allocator that we can use at this early stage of boot? I.e. would alloc_pages() maybe work?
How do other subsystems that rely on dynamic allocation for registering their resources handle this? I guess regulator must fall in the same use-case, doesn't it?
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