linux-kernel - Re: [PATCH v5 01/10] interconnect: qcom: rpm: make QoS INVALID default, separate out driver data

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Date:   Thu, 23 Feb 2023 13:01:45 +0000
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Georgi Djakov <djakov@...nel.org>,
        Evan Green <evgreen@...omium.org>,
        Jun Nie <jun.nie@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Brian Masney <masneyb@...tation.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Yassine Oudjana <y.oudjana@...tonmail.com>
Cc:     Georgi Djakov <georgi.djakov@...aro.org>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 01/10] interconnect: qcom: rpm: make QoS INVALID
 default, separate out driver data

On 17/02/2023 10:46, Konrad Dybcio wrote:

I find this commit log difficult to understand.

Could you reduce it down ?

> Currently, NOC_QOS_MODE_FIXED is defined as 0x0, which makes it the
> "default" option (as that's what uninitialized members of partially
> initialized structs are set to), which should really have been
> NOC_QOS_MODE_INVALID, and that's what people (wrongly) assumed was
> the case when .qos.qos_mode was not defined and what really makes
> the most sense..

"Currently NOC_QOS_MODE_FIXED is defined as 0x0 which makes it the 
default option. The default option however should be NOC_QOS_MODE_INVALID"

> That resulted in {port 0, prio 0, areq_prio 0, urg_fwd = false, rpm-voted}
> QoS being always voted for, because the code flow assumed "hey, it's fixed
> QoS, so let's just roll with whatever parameters are set" [again, set by
> partial struct initialization, as these fields were left unfilled by the
> developers]. That is of course incorrect, and on many of these platforms
> port 0 is MAS_APPS_PROC, which 9/10 times is supposed to be handled by
> the ap_owned path, not to mention the rest of the parameters may differ.
> Arguably, the APPS node is the most important one, next to EBI0..

This paragraph in particular is difficult to decipher, at least for me 
with my native Dublinese


> The modes are defined as preprocessor constants. They are not used
> anywhere outside the driver or sent to any remote processor outside
> qcom_icc_set_noc_qos(), which is easily worked around.
> Separate the type specified in driver data from the value sent to msmbus.
> Make the former an enum for better mainainability.
> 
> This is an implicit fix for every SMD RPM ICC driver that didn't
> explicitly specify NOC_QOS_MODE_INVALID on non-AP_owned nodes that
> don't have QoS settings.

It would be nice to reduce the commit log down to say three paragraphs 
of no more than three sentences each.

---
bod