Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <00b817a4-f1ac-6a94-5f1e-836d8d313406@linaro.org>
Date:   Mon, 25 Oct 2021 17:03:52 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.1.1
Subject: Re: [PATCH] media: venus: Synchronize probe() between venus_core and
 enc/dec
Content-Language: en-US
To:     Tadeusz Struk <tadeusz.struk@linaro.org>,
        Stanimir Varbanov <stanimir.varbanov@linaro.org>,
        Andy Gross <agross@kernel.org>
Cc:     Bjorn Andersson <bjorn.andersson@linaro.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Lee Jones <lee.jones@linaro.org>,
        Amit Pundir <amit.pundir@linaro.org>,
        John Stultz <john.stultz@linaro.org>,
        linux-media@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20211025144345.267107-1-tadeusz.struk@linaro.org>
 <72f8dd7a-66c7-fb50-db23-f98ba753af1d@nexus-software.ie>
 <bba3acc1-cfa1-0c53-75de-f4ffa0a2bc9e@linaro.org>
From:   Bryan O'Donoghue <bryan.odonoghue@linaro.org>
In-Reply-To: <bba3acc1-cfa1-0c53-75de-f4ffa0a2bc9e@linaro.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 25/10/2021 16:30, Tadeusz Struk wrote:
> No, we want a hard stop here. At this point the venus_core probe()
> has finished and it failed. Returning -EPROBE_DEFER here will just
> cause it to loop infinitely.

I don't think there's any guarantee at all, that core probe() has 
completed at that point.

of_platform_populate() doesn't guarantee ordering of the probe() 
completing before or after the probe() of the platform drivers that are 
associated with the devices in of_platform_populate().

When you think it about it can't do that and you wouldn't want it to do 
that since a device might have a legitimate reason to EPROBE_DEFER

As an example core could call of_platform_populate() and then as a 
ridiculous example go to sleep for five seconds - in which case it is 
perfectly possible the encoder and decoder probe() functions will bug 
out illegitimately waiting because of core->state != CORE_INIT

This is a problem we have and still haven't solved in 
drivers/usb/dwc3/dwc3-qcom.c::probe() and child devices 
drivers/usb/dwc3/dwc3-qcom.c

Here:
https://patches.linaro.org/cover/470387/

There's no serialisation guarantee between parent and child on 
of_platform_populate() - at least none I'm aware of.

---
bod