linux-kernel - Re: [PATCH V2 1/3] ufs: core: Add CPU latency QoS support for ufs driver

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Message-ID: <20231206153242.GI12802@thinkpad>
Date:   Wed, 6 Dec 2023 21:02:42 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Naresh Maramaina <quic_mnaresh@...cinc.com>
Cc:     Bart Van Assche <bvanassche@....org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Peter Wang <peter.wang@...iatek.com>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, chu.stanley@...il.com,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, quic_cang@...cinc.com,
        quic_nguyenb@...cinc.com, Nitin Rawat <quic_nitirawa@...cinc.com>
Subject: Re: [PATCH V2 1/3] ufs: core: Add CPU latency QoS support for ufs
 driver

On Wed, Dec 06, 2023 at 07:32:54PM +0530, Naresh Maramaina wrote:
> 
> 
> On 12/5/2023 10:41 PM, Bart Van Assche wrote:
> > On 12/4/23 21:58, Naresh Maramaina wrote:
> > > On 12/5/2023 12:30 AM, Bart Van Assche wrote:
> > > > On 12/4/23 06:30, Maramaina Naresh wrote:
> > > > > +    /* This capability allows the host controller driver to
> > > > > use the PM QoS
> > > > > +     * feature.
> > > > > +     */
> > > > > +    UFSHCD_CAP_PM_QOS                = 1 << 13,
> > > > >   };
> > > > 
> > > > Why does it depend on the host driver whether or not PM QoS is
> > > > enabled? Why isn't it enabled unconditionally?
> > > 
> > > For some platform vendors power KPI might be more important than
> > > random io KPI. Hence this flag is disabled by default and can be
> > > enabled based on platform requirement.
> > 
> > How about leaving this flag out unless if a host vendor asks explicitly
> > for this flag?
> 
> IMHO, instead of completely removing this flag, how about having
> flag like "UFSHCD_CAP_DISABLE_PM_QOS" which will make PMQOS enable
> by default and if some host vendor wants to disable it explicitly,
> they can enable that flag.
> Please let me know your opinion.
> 

If a vendor wants to disable this feature, then the driver has to be modified.
That won't be very convenient. So either this has to be configured through sysfs
or Kconfig if flexibility matters.

- Mani

> > > > 
> > > > > + * @pm_qos_req: PM QoS request handle
> > > > > + * @pm_qos_init: flag to check if pm qos init completed
> > > > >    */
> > > > 
> > > > Documentation for pm_qos_init is missing.
> > > > 
> > > Sorry, i didn't get your comment, i have already added documentation
> > > for @pm_qos_init, @pm_qos_req variable as above. Do you want me to
> > > add this information some where else as well?
> > 
> > Oops, I meant 'qos_vote'.
> 
> Sure. I'll take of this in next patchset.
> 
> > 
> > Thanks,
> > 
> > Bart.
> > 
> 
> Thanks,
> Naresh
> 

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