Re: [PATCH v2 09/15] scsi: ufs: deprecate 'freq-table-hz' property

From: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
To: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Alim Akhtar <alim.akhtar@samsung.com>,
	Avri Altman <avri.altman@wdc.com>,
	Rob Herring <robh+dt@kernel.org>, Andy Gross <agross@kernel.org>,
	Wei Xu <xuwei5@hisilicon.com>, Nishanth Menon <nm@ti.com>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Tero Kristo <kristo@kernel.org>,
	"James E.J. Bottomley" <jejb@linux.ibm.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Jan Kotas <jank@cadence.com>, Li Wei <liwei213@huawei.com>,
	Stanley Chu <stanley.chu@mediatek.com>,
	Yaniv Gardi <ygardi@codeaurora.org>,
	linux-scsi@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-samsung-soc@vger.kernel.org,
	linux-mediatek@lists.infradead.org
Subject: Re: [PATCH v2 09/15] scsi: ufs: deprecate 'freq-table-hz' property
Date: Wed, 23 Feb 2022 10:15:36 +0100	[thread overview]
Message-ID: <455a8a87-63e7-7864-f765-142be18d1fa8@canonical.com> (raw)
In-Reply-To: <YhUodbzxx4wbr+gy@ripper>

On 22/02/2022 19:16, Bjorn Andersson wrote:
> On Tue 22 Feb 06:58 PST 2022, Krzysztof Kozlowski wrote:
> 
>> The 'freq-table-hz' is not correct in DT schema, because '-hz' suffix
>> defines uint32 type, not an array.  Therefore deprecate 'freq-table-hz'
>> and use 'freq-table' instead.
>>
> 
> Patch looks good in itself, but why don't we use opp-table to describe
> the performance states?
> 
> In particular looking at the two columns of frequencies for various
> Qualcomm boards they require different performance-states.
> 
> A concrete example is sm8350.dtsi, which specifies 75MHz and 300MHz as
> the first frequency pair. The lower level requires the VDD_CX power rail
> to be at least &rpmhpd_opp_low_svs, the higher frequency has a
> required-opps of &rpmhpd_opp_nom.
> 
> 
> As this isn't possible to express in the current binding we've just been
> forced to always run at a higher voltage level and kept this in the todo
> list.
> 
> But rather than migrating freq-table-hz to freq-table and then having to
> introduce an opp table to express the power constraints, could we
> perhaps skip the intermediate step?
> 
> Or would you have any other suggestion about how we can represent the
> required-opps level together with the freq-table (if that's what we want
> to stick with).

Usage of OPP tables is interesting solution. It would solve your problem
of power rail levels. This would need several opp-tables - one for each
clock, which is not a big problem.

The problem is that I do not have any UFS hardware (none of my Samsung
Exynos boards have UFS... I don't have even arm64 Exynos chips :( ), so
implementing it theoretically will be painful.
OTOH, I believe that having a working dtschema is very useful. Having
dtschema without errors/warnings is even worth some churn/intermediary work.

The intermediary work is also not that big. Once proper OPP is
implemented, we will have "just" two deprecated properties in the bindings.

Best regards,
Krzysztof