linux-kernel - Re: [RFT PATCH 1/9] drivers: qcom: rpmh-rsc: Clean code reading/writing regs/cmds

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Message-ID: <158395500244.149997.1358582842144222001@swboyd.mtv.corp.google.com>
Date:   Wed, 11 Mar 2020 12:30:02 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Doug Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>
Cc:     Maulik Shah <mkshah@...eaurora.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Evan Green <evgreen@...omium.org>,
        Lina Iyer <ilina@...eaurora.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFT PATCH 1/9] drivers: qcom: rpmh-rsc: Clean code reading/writing regs/cmds

Quoting Matthias Kaehlcke (2020-03-11 09:17:26)
> Hi,
> 
> On Wed, Mar 11, 2020 at 08:03:27AM -0700, Doug Anderson wrote:
> > Hi,
> > 
> > On Wed, Mar 11, 2020 at 1:47 AM Maulik Shah <mkshah@...eaurora.org> wrote:
> > >
> > > Hi,
> > >
> > > On 3/7/2020 5:29 AM, Douglas Anderson wrote:
> > > > This patch makes two changes, both of which should be no-ops:
> > > >
> > > > 1. Make read_tcs_reg() / read_tcs_cmd() symmetric to write_tcs_reg() /
> > > >    write_tcs_cmd().
> > >
> > > i agree that there are two different write function doing same thing except last addition (RSC_DRV_CMD_OFFSET * cmd_id)
> > >
> > > can you please rename write_tcs_cmd() to write_tcs_reg(), add above operation in it, and then remove existing write_tcs_reg().
> > > this way we have only one read and one write function.
> > >
> > > so at the end we will two function as,
> > >
> > > static u32 read_tcs_reg(struct rsc_drv *drv, int reg, int tcs_id, int cmd_id)
> > > {
> > >         return readl_relaxed(drv->tcs_base + reg + RSC_DRV_TCS_OFFSET * tcs_id +
> > >                              RSC_DRV_CMD_OFFSET * cmd_id);
> > > }
> > >
> > > static void write_tcs_reg(struct rsc_drv *drv, int reg, int tcs_id, int cmd_id,
> > >                           u32 data)
> > > {
> > >         writel_relaxed(data, drv->tcs_base + reg + RSC_DRV_TCS_OFFSET * tcs_id +
> > >                        RSC_DRV_CMD_OFFSET * cmd_id);
> > > }
> > 
> > I can if you insist and this is still better than the existing
> > (inconsistent) code.
> > 
> > ...but I still feel that having two functions adds value here.
> > 
> > 
> > Anyone else who is CCed want to weigh in and tie break?
> 
> I agree with Doug, having two functions makes the code that calls them
> clearer. It makes it evident when a command is read/written and doesn't require
> a useless extra parameter when accessing a non-command register.

Me too! In fact, I asked for this when this driver was introduced and I
was half-ignored[1]. Making sure we never have to pass 0 to one of these
functions should be a goal.

>From two years ago:
>
> Is m the type of TCS (sleep, active, wake) and n is just an offset?
> Maybe you can replace m with 'tcs_type' and n with 'index' or 'i' or
> 'offset'. And then don't use this function to write the random TCS
> registers that don't have to do with the TCS command slots? I see
> various places where there are things like:
> 
> > +               write_tcs_reg(drv, RSC_DRV_CMD_ENABLE, m, 0, 0);
> > +       write_tcs_reg(drv, RSC_DRV_CMD_WAIT_FOR_CMPL, m, 0, cmd_complete);
> > +       write_tcs_reg(drv, RSC_DRV_CMD_ENABLE, m, 0, cmd_enable);
> 
> And 'n' is 0, meaning you rely on that 0 killing that last part of the
> equation (RSC_DRV_CMD_OFFSET * n). But if we had a write_tcs_reg(drv,
> reg, m, data) and a write_tcs_cmd(drv, reg, m, n, data) then it would be
> clearer.
> 
> Even better, add a void *base to a 'struct tcs' and then pass that
> struct to the tcs_read/write APIs and then have that pull out a
> tcs->base + reg or tcs->base + reg + RSC_DRV_CMD_OFFSET * index.
> 

[1] https://lore.kernel.org/linux-arm-msm/152364140661.51482.261490347611407195@swboyd.mtv.corp.google.com/