Re: [PATCH v4] amba: Remove deferred device addition

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2022/7/5 16:39, Saravana Kannan wrote:
> The uevents generated for an amba device need PID and CID information
> that's available only when the amba device is powered on, clocked and
> out of reset. So, if those resources aren't available, the information
> can't be read to generate the uevents. To workaround this requirement,
> if the resources weren't available, the device addition was deferred and
> retried periodically.
>
> However, this deferred addition retry isn't based on resources becoming
> available. Instead, it's retried every 5 seconds and causes arbitrary
> probe delays for amba devices and their consumers.
>
> Also, maintaining a separate deferred-probe like mechanism is
> maintenance headache.
>
> With this commit, instead of deferring the device addition, we simply
> defer the generation of uevents for the device and probing of the device
> (because drivers needs PID and CID to match) until the PID and CID
> information can be read. This allows us to delete all the amba specific
> deferring code and also avoid the arbitrary probing delays.
>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Ulf Hansson <ulf.hansson@linaro.org>
> Cc: John Stultz <john.stultz@linaro.org>
> Cc: Saravana Kannan <saravanak@google.com>
> Cc: Linus Walleij <linus.walleij@linaro.org>
> Cc: Sudeep Holla <sudeep.holla@arm.com>
> Cc: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> Cc: Geert Uytterhoeven <geert+renesas@glider.be>
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>
> Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
> Cc: Russell King <linux@armlinux.org.uk>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
> ---
>
> v1 -> v2:
> - Dropped RFC tag
> - Complete rewrite to not use stub devices.
>
> v2 -> v3:
> - Flipped the if() condition for hard-coded periphids.
> - Added a stub driver to handle the case where all amba drivers are
>    modules loaded by uevents.
> - Cc Marek after I realized I forgot to add him.
>
> v3 -> v4:
> - Finally figured out and fixed the issue reported by Kefeng (bus match
>    can't return an error other than -EPROBE_DEFER).
> - I tested the patch on "V2P-CA15" on qemu
> - Marek tested v3, but that was so long ago and the rebase wasn't clean,
>    so I didn't include the tested-by.
>
> Marek/Kefeng,
>
> Mind giving a Tested-by?

Hi Saravana, I tested on my qemu, and previous panic[1] disappeared, so

Tested-by: Kefeng Wang <wangkefeng.wang@huawei.com>

[1] 
https://lore.kernel.org/linux-arm-kernel/CAGETcx8RLor0JcboBuMrB96xUot14P1CAcqoen7ZHnYRi7KMEQ@mail.gmail.com/