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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 11 Mar 2020 09:17:26 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Doug Anderson <dianders@...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>,
        Stephen Boyd <swboyd@...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

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.

> > > 2. Change the order of operations in the above functions to make it
> > >    more obvious to me what the math is doing.  Specifically first you
> > >    want to find the right TCS, then the right register, and then
> > >    multiply by the command ID if necessary.
> > With above change, i don't think you need to re-order this.
> > specifically from tcs->base, we find right "reg" first and if it happens to be tcs then intended tcs, and then cmd inside tcs.
> 
> There was never any "need" to re-order.  That math works out to be the
> same.  This is just clearer.
> 
> As an example, let's look at this:
> 
> struct point {
>   int x;
>   int y;
> };
> struct point points[10];
> 
> Let's say you have:
>   void *points_base = &(points[0]);
> 
> ...and now you want to find &(points[5].y).  What does your math look like?
> 
> a) points_base + (sizeof(struct point) * 5) + 4 ;
> 
> ...or...
> 
> b) points_base + 4 + (sizeof(struct point) * 5);
> 
> 
> Both calculations give the same result, but I am arguring that "a)" is
> more intuitive.  Specifically you deal with the array access first and
> then deal with the offset within the structure that you found.

+1