linux-kernel - Re: [PATCH v5 1/2] scsi: ufs: Do not disable vccq in UFSHC driver

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Date:   Wed, 13 Feb 2019 11:05:28 +0100
From:   Marc Gonzalez <marc.w.gonzalez@...e.fr>
To:     Mark Brown <broonie@...nel.org>
Cc:     SCSI <linux-scsi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Jeffrey Hugo <jhugo@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Evan Green <evgreen@...omium.org>,
        Douglas Anderson <dianders@...omium.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        Pedro Sousa <pedrom.sousa@...opsys.com>,
        Joao Pinto <jpinto@...opsys.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Bart Van Assche <bart.vanassche@....com>,
        Stanislav Nijnikov <stanislav.nijnikov@....com>,
        Alex Lemberg <alex.lemberg@....com>,
        Ohad Sharabi <ohad.sharabi@....com>,
        Venkat Gopalakrishnan <venkatg@...eaurora.org>,
        Subhash Jadavani <subhashj@...eaurora.org>,
        Yaniv Gardi <ygardi@...eaurora.org>,
        Raviv Shvili <rshvili@...eaurora.org>,
        Hannes Reinecke <hare@...e.de>, Kyuho Choi <kyuho.choi@...com>,
        Martin Petersen <martin.petersen@...cle.com>
Subject: Re: [PATCH v5 1/2] scsi: ufs: Do not disable vccq in UFSHC driver

On 11/02/2019 18:23, Mark Brown wrote:

> On Mon, Feb 11, 2019 at 02:32:15PM +0100, Marc Gonzalez wrote:
> 
>> Unfortunately, this optimization breaks UFS on systems where vccq
>> powers not only the Flash chip, but the host controller as well,
>> such as APQ8098 MEDIABOX or MTP8998.
>> 
>> In my opinion, the rationale for the original patch is questionable.
>> If neither the UFSHC, nor the Flash chip, require any load from vccq,
>> then that power rail should simply not be specified at all in the DT.
> 
> If the supply is physically connected it should be valid to represent
> this in DT regardless of how or if the supply gets used at runtime.
> However it does sound like this support needs to be better thought
> through to make sure we have represented the supplies to the flash chip
> and the controller separately - it seems like right now there's no
> tracking of the supplies needed for the controller and the assumption is
> that only the flash chip needs managing which is breaking things.

As far as I'm aware, the conflation of host controller with their respective
storage medium occurs across several techs: UFS, NAND, SDHC, EMMC.

There might be room for improvement, but I don't think these considerations
should hold up this series, which fixes something that is broken *today*.

UFS reviewers (Alim, Avri, Pedro), can I get at least one Acked-by to remove
this small power optimization that breaks UFS on my system?

Regards.