linux-kernel - Re: [PATCH 3/6] firmware: qcom: scm: Handle various probe ordering for qcom_scm_assign

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Message-ID: <a5343627-a325-465e-b744-747d4c1b2cae@linaro.org>
Date: Wed, 20 Nov 2024 15:19:00 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Bartosz Golaszewski <brgl@...ev.pl>
Cc: Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, Mukesh Ojha
 <quic_mojha@...cinc.com>, Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Stephan Gerhold <stephan.gerhold@...aro.org>,
 Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
 Kuldeep Singh <quic_kuldsing@...cinc.com>,
 Elliot Berman <quic_eberman@...cinc.com>,
 Andrew Halaney <ahalaney@...hat.com>,
 Avaneesh Kumar Dwivedi <quic_akdwived@...cinc.com>,
 Andy Gross <andy.gross@...aro.org>, linux-arm-msm@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] firmware: qcom: scm: Handle various probe ordering
 for qcom_scm_assign_mem()

On 20/11/2024 15:07, Bartosz Golaszewski wrote:
>> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
>> index 5d91b8e22844608f35432f1ba9c08d477d4ff762..93212c8f20ad65ecc44804b00f4b93e3eaaf8d95 100644
>> --- a/drivers/firmware/qcom/qcom_scm.c
>> +++ b/drivers/firmware/qcom/qcom_scm.c
>> @@ -1075,6 +1075,9 @@ int qcom_scm_assign_mem(phys_addr_t mem_addr, size_t mem_sz,
>>         int ret, i, b;
>>         u64 srcvm_bits = *srcvm;
>>
>> +       if (!qcom_scm_is_available())
>> +               return -EPROBE_DEFER;
>> +
> 
> Should we be returning -EPROBE_DEFER from functions that are not
> necessarily limited to being used in probe()? For instance ath10k uses
> it in a workqueue job. I think this is why this driver is probed in
> subsys_initcall() rather than module_initcall().
Uh, good point. To my understanding, every resource like function can do
it, e.g. clk_get. Whether drivers call it in probe() or somewhere else -
e.g. some startup call like there is plenty in the ASoC or DMA
device_alloc_chan_resources() - is responsibility of the
driver/consumer, not the provider of that resource.

With such explanation returning EPROBE_DEFER is ok, just like returning
anything else (e.g. EINVAL).

Now about this function: it is not exactly "get a resource" one, but
still the caller might want to call it again later, which is implied by
EPROBE_DEFER. Maybe this should be EAGAIN instead? Just like
power-supply is doing in power_supply_get_property().

Best regards,
Krzysztof