[Buildroot] [PATCH] wf111: Add mdev dependency

[Floris Bos <bos@je-eigen-domein.nl>]

On 08/12/2015 10:49 PM, Charles Manning wrote:
> On Wed, Aug 12, 2015 at 10:29 PM, Floris Bos <bos@je-eigen-domein.nl> wrote:
>> On 08/11/2015 09:17 AM, Charles Manning wrote:
>>> wf111 really needs mdev
>>
>> Problem I have seen with mdev in its default configuration is that it
>> doesn't just handle firmware load requests, but also takes it upon itself to
>> create/delete the device nodes (even when that already is being handled by
>> devtmpfs), and does a bad job with that.
>>
>> It doesn't preserve sequencing by default, and events are processed
>> concurrently, and get out-of-order.
>>
>> Becomes a problem if your software for example does anything that causes the
>> kernel to re-read the partition table of your storage.
>> In that case the kernel sends events to delete all devices nodes of the
>> storage device, and add them again, right after each other.
>> However depending on your luck, they can get processed in reverse order:
>>
>> ==
>> mdev[598]: 9.191594 ACTION:add SUBSYSTEM:block DEVNAME:mmcblk0p6
>> DEVPATH:/devices/platform/soc/3f300000.mmc/mmc_host/mmc0/mmc0:1234/block/mmcblk0/mmcblk0p6
>> mdev[598]: dev 179,6
>> [...]
>> mdev[593]: 9.192168 ACTION:remove SUBSYSTEM:block DEVNAME:mmcblk0p6
>> DEVPATH:/devices/platform/soc/3f300000.mmc/mmc_host/mmc0/mmc0:1234/block/mmcblk0/mmcblk0p6
>> mdev[593]: rule matched, line -1
>> mdev[593]: unlink: mmcblk0p6
>> ==
>>
>> Add is processed before remove, with the end result that /dev/mmcblk0p6 goes
>> missing...
>>
>>
>> So please don't pull in mdev automatically just for firmware loading,
>> because it does more than just that, and can have serious side effects.
> Ok, now I'm stumped. People are telling me "don't use mdev", but
> nobody is providing a viable alternative.
>
> The situation is this:
> * I did not write wf111, it is not as if I am submitting a new package.
> * We have an existing package wf111.
> * The existing package does not work (ie. does not do fw loading)
> unless there is mdev or udev. Without fw loading wf111 is broken.

Suggest you double check there isn't a newer kernel version available 
for your target device.
Pretty sure newer kernels can also load the firmware straight from 
/lib/firmware without userspace helper.


Yours sincerely,

Floris Bos