From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Boyd Subject: Re: [PATCH v9 07/22] clk: Add API to get index of the clock parent Date: Thu, 07 Nov 2019 11:19:32 -0800 Message-ID: <20191107191933.0B18021D6C@mail.kernel.org> References: <1565984527-5272-1-git-send-email-skomatineni@nvidia.com> <1565984527-5272-8-git-send-email-skomatineni@nvidia.com> <20191106231005.F2CD820869@mail.kernel.org> <20191107152115.GA2580600@ulmo> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <20191107152115.GA2580600@ulmo> Sender: linux-kernel-owner@vger.kernel.org To: Dmitry Osipenko , Thierry Reding Cc: Sowjanya Komatineni , jason@lakedaemon.net, jonathanh@nvidia.com, linus.walleij@linaro.org, marc.zyngier@arm.com, mark.rutland@arm.com, stefan@agner.ch, tglx@linutronix.de, pdeschrijver@nvidia.com, pgaikwad@nvidia.com, linux-clk@vger.kernel.org, linux-gpio@vger.kernel.org, jckuo@nvidia.com, josephl@nvidia.com, talho@nvidia.com, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, mperttunen@nvidia.com, spatra@nvidia.com, robh+dt@kernel.org, devicetree@vger.kernel.org, rjw@rjwysocki.net, viresh.kumar@linaro.org, linux-pm@vger.kernel.org List-Id: linux-tegra@vger.kernel.org Quoting Thierry Reding (2019-11-07 07:21:15) > On Thu, Nov 07, 2019 at 03:54:03AM +0300, Dmitry Osipenko wrote: > > 07.11.2019 02:10, Stephen Boyd =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > > > Quoting Sowjanya Komatineni (2019-08-16 12:41:52) > > >> This patch adds an API clk_hw_get_parent_index to get index of the > > >> clock parent to use during the clock restore operations on system > > >> resume. > > > =20 > > > Is there a reason we can't save the clk hw index at suspend time by > > > reading the hardware to understand the current parent? The parent ind= ex > > > typically doesn't matter unless we're trying to communicate something > > > from the framework to the provider driver. Put another way, I would > > > think the provider driver can figure out the index itself without hav= ing > > > to go through the framework to do so. > >=20 > > Isn't it a bit wasteful to duplicate information about the parent within > > a provider if framework already has that info? The whole point of this > > new API is to allow providers to avoid that unnecessary duplication. > >=20 > > Please note that clk_hw_get_parent_index is getting used only at the > > resume time and not at suspend. >=20 > I agree with this. All of the information that we need is already cached > in the framework. Doing this in the driver would mean essentially adding > a "saved parent" field along with code to read the value at suspend time > to the three types of clocks that currently use this core helper. Don't we already have a "saved parent" field by storing the pointer to the clk_hw? >=20 > That's certainly something that we *can* do, but it doesn't sound like a > better option than simply querying the framework for the value that we > need. >=20 Let me say this another way. Why does this driver want to know the index that the framework uses for some clk_hw pointer? Perhaps it happens to align with the same value that hardware uses, but I still don't understand why the driver wants to know what the framework has decided is the index for some clk_hw pointer. Or is this something like "give me the index for the parent that the framework thinks I currently have but in reality don't have anymore because the register contents were wiped and we need to reparent it"? A generic API to get any index for this question is overkill and we should consider adding some sort of API like clk_hw_get_current_parent_index(), or a framework flag that tells the framework this parent is incorrect and we need to call the .set_parent() op again to reconfigure it.