linux-kernel - Re: [PATCH v9 4/9] soc: mediatek: Add multiple step bus protection control

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Date:   Thu, 19 Dec 2019 11:42:18 +0800
From:   Nicolas Boichat <drinkcat@...omium.org>
To:     Weiyi Lu <weiyi.lu@...iatek.com>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Rob Herring <robh@...nel.org>,
        James Liao <jamesjj.liao@...iatek.com>,
        Fan Chen <fan.chen@...iatek.com>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        srv_heupstream <srv_heupstream@...iatek.com>,
        Yong Wu <yong.wu@...iatek.com>
Subject: Re: [PATCH v9 4/9] soc: mediatek: Add multiple step bus protection control

On Wed, Dec 18, 2019 at 10:25 AM Weiyi Lu <weiyi.lu@...iatek.com> wrote:
>
> On Tue, 2019-12-17 at 13:33 +0800, Nicolas Boichat wrote:
> > On Tue, Dec 17, 2019 at 10:51 AM Weiyi Lu <weiyi.lu@...iatek.com> wrote:
> > >
> > > On Mon, 2019-12-16 at 15:21 +0800, Nicolas Boichat wrote:
> > > > On Tue, Dec 10, 2019 at 2:47 PM Weiyi Lu <weiyi.lu@...iatek.com> wrote:
> > > > >
> > > > > Both MT8183 & MT6765 have more control steps of bus protection
> > > > > than previous project. And there add more bus protection registers
> > > > > reside at infracfg & smi-common. Also add new APIs for multiple
> > > > > step bus protection control with more customized arguments.
> > > > >
> > > > > Signed-off-by: Weiyi Lu <weiyi.lu@...iatek.com>
> > > > > ---
> > > > >  drivers/soc/mediatek/Makefile           |  2 +-
> > > > >  drivers/soc/mediatek/mtk-scpsys-ext.c   | 99 +++++++++++++++++++++++++++++++++
> > > > >  drivers/soc/mediatek/mtk-scpsys.c       | 39 +++++++++----
> > > > >  include/linux/soc/mediatek/scpsys-ext.h | 39 +++++++++++++
> > > > >  4 files changed, 168 insertions(+), 11 deletions(-)
> > > > >  create mode 100644 drivers/soc/mediatek/mtk-scpsys-ext.c
> > > > >  create mode 100644 include/linux/soc/mediatek/scpsys-ext.h
> > > > >
> > > > > diff --git a/drivers/soc/mediatek/Makefile b/drivers/soc/mediatek/Makefile
> > > > > index b017330..b442be9 100644
> > > > > --- a/drivers/soc/mediatek/Makefile
> > > > > +++ b/drivers/soc/mediatek/Makefile
> > > > > @@ -1,5 +1,5 @@
> > > > >  # SPDX-License-Identifier: GPL-2.0-only
> > > > >  obj-$(CONFIG_MTK_CMDQ) += mtk-cmdq-helper.o
> > > > > -obj-$(CONFIG_MTK_INFRACFG) += mtk-infracfg.o
> > > > > +obj-$(CONFIG_MTK_INFRACFG) += mtk-infracfg.o mtk-scpsys-ext.o
> > > > >  obj-$(CONFIG_MTK_PMIC_WRAP) += mtk-pmic-wrap.o
> > > > >  obj-$(CONFIG_MTK_SCPSYS) += mtk-scpsys.o
> > > > > diff --git a/drivers/soc/mediatek/mtk-scpsys-ext.c b/drivers/soc/mediatek/mtk-scpsys-ext.c
> > > > > new file mode 100644
> > > > > index 0000000..4f1adda
> > > > > --- /dev/null
> > > > > +++ b/drivers/soc/mediatek/mtk-scpsys-ext.c
> > > > > @@ -0,0 +1,99 @@
> > > > > +// SPDX-License-Identifier: GPL-2.0
> > > > > +/*
> > > > > + * Copyright (c) 2018 MediaTek Inc.
> > > > > + * Author: Owen Chen <Owen.Chen@...iatek.com>
> > > > > + */
> > > > > +#include <linux/ktime.h>
> > > > > +#include <linux/mfd/syscon.h>
> > > > > +#include <linux/of_device.h>
> > > > > +#include <linux/regmap.h>
> > > > > +#include <linux/soc/mediatek/scpsys-ext.h>
> > > > > +
> > > > > +#define MTK_POLL_DELAY_US   10
> > > > > +#define MTK_POLL_TIMEOUT    USEC_PER_SEC
> > > > > +
> > > > > +static int set_bus_protection(struct regmap *map, u32 mask, u32 ack_mask,
> > > > > +               u32 reg_set, u32 reg_sta, u32 reg_en)
> > > > > +{
> > > > > +       u32 val;
> > > > > +
> > > > > +       if (reg_set)
> > > > > +               regmap_write(map, reg_set, mask);
> > > > > +       else
> > > > > +               regmap_update_bits(map, reg_en, mask, mask);
> > > >
> > > > At least for 8183, we never seen to use the reg_set case, can we
> > > > simplify this function?
> > > >
> > >
> > > Actually 6765 will use it and all the other MediaTek chips at least in
> > > near future.
> > > https://patchwork.kernel.org/patch/11042003/
> >
> > Ok, that's fine then.
> >
> > > > > +
> > > > > +       return regmap_read_poll_timeout(map, reg_sta,
> > > > > +                       val, (val & ack_mask) == ack_mask,
> > > > > +                       MTK_POLL_DELAY_US, MTK_POLL_TIMEOUT);
> > > >
> > > > From 8183, I see that you have either:
> > > >  1. mask == ack_mask
> > > >  2. ack_mask == 0 (essentially this skips this test)
> > > >
> > > > Would it be simpler to just skip this test if reg_sta == 0, and always
> > > > assume mask == ack_mask otherwise?
> > > >
> > > > e.g.
> > > > if (reg_sta == 0)
> > > >    return 0;
> > > >
> > > > return regmap_read_poll_timeout(map, reg_sta,
> > > >                        val, (val & mask) == mask,
> > > >                        MTK_POLL_DELAY_US, MTK_POLL_TIMEOUT);
> > > >
> > >
> > > I'm not sure if you mean ack_mask == 0?
> > > reg_sta would be possible to be 0 because it's a register address
> > > offset.
> >
> > Right, so maybe "0" is not a good invalid value, or maybe you can have a
> > #define REG_STA_INVALID U32_MAX
> >
> > And then test for:
> > if (reg_sta == REG_STA_INVALID)
> >    return 0;
> >
> > My point here is that mask and ack_mask are always the same (unless
> > you don't care about reading back the status), so maybe you only need
> > to specify mask?
> >
> > (but if you need different mask and ack_mask for future chips, feel
> > free to ignore)
> >
>
> I do need different mask and ack_mask.
> For the special case of 8183 here, we still have to check the ack status
> when setting bus protection but only ignore the ack status when clearing
> bus protection.
>
> case A.
> SET: reg_set, reg_sta, mask == ack mask
> CLEAR: reg_clr, reg_sta, mask == clear ack mask
>
> case B. (the special case we discussed)
> SET: reg_set, reg_sta, mask == ack mask
> CLEAR: reg_clr, reg_sta, mask != clear ack mask(which is 0 now)
>
> If I use the REG_STA_INVALID to replace the clear ack mask way.
> I might need two reg_sta to satisfy the check of set and clear bus
> protection.
> One is valid for setting case and another is invalid for clearing case,
> e.g. case 2 below
>
> case 1.
> SET: reg_set, reg_sta(valid), mask == ack mask
> CLEAR: reg_clr, reg_sta(valid), mask == ack mask
>
> case 2.
> SET: reg_set, reg_sta(valid), mask == ack mask
> CLEAR: reg_clr, reg_sta(invalid then return), mask == ack mask
>
> so I'd like to keep the original proposal. What do you think?

Ooh, I see. This is quite confusing to be honest... I wonder if it
wouldn't be clearer to have a boolean instead in bus_prot (something
like "clk_no_check", can't find a better name right now).