Message-ID: <1450245647.22854.109.camel@mhfsdcap03>
Date:	Wed, 16 Dec 2015 14:00:47 +0800
From:	Yong Wu <yong.wu@...iatek.com>
To:	Daniel Kurtz <djkurtz@...omium.org>
CC:	Matthias Brugger <matthias.bgg@...il.com>,
	Joerg Roedel <joro@...tes.org>,
	Thierry Reding <treding@...dia.com>,
	Mark Rutland <mark.rutland@....com>,
	Robin Murphy <robin.murphy@....com>,
	Will Deacon <will.deacon@....com>,
	Tomasz Figa <tfiga@...gle.com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Rob Herring <robh+dt@...nel.org>,
	"Catalin Marinas" <catalin.marinas@....com>,
	<linux-mediatek@...ts.infradead.org>,
	Sasha Hauer <kernel@...gutronix.de>,
	srv_heupstream <srv_heupstream@...iatek.com>,
	"open list:OPEN FIRMWARE AND..." <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
	Paul Bolle <pebolle@...cali.nl>,
	"Arnd Bergmann" <arnd@...db.de>, <mitchelh@...eaurora.org>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>
Subject: Re: [PATCH v6 3/5] memory: mediatek: Add SMI driver

On Tue, 2015-12-15 at 13:45 +0800, Daniel Kurtz wrote:
> Hi Yong,
> 
> On Tue, Dec 15, 2015 at 10:38 AM, Yong Wu <yong.wu@...iatek.com> wrote:
> > On Mon, 2015-12-14 at 19:18 +0100, Matthias Brugger wrote:
> >> On Tuesday 08 Dec 2015 17:49:11 Yong Wu wrote:
> >> > This patch add SMI(Smart Multimedia Interface) driver. This driver
> >> > is responsible to enable/disable iommu and control the power domain
> >> > and clocks of each local arbiter.
> >> >
> >> > Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> >> > ---
> >> >   Currently SMI offer mtk_smi_larb_get/put to enable the power-domain
> >> > ,clocks and initialize the iommu configuration register for each a local
> >> > arbiter, The reason is:
> >> >   a) If a device would like to disable iommu, it also need call
> >> > mtk_smi_larb_get/put to enable its power and clocks.
> >> >   b) The iommu core don't support attach/detach a device within a
> >> > iommu-group. So we cann't use iommu_attach_device(iommu_detach_device)
> >> > instead
> >> > of mtk_smi_larb_get/put.
> >> >
> > [..]
> >> > +static int
> >> > +mtk_smi_enable(struct device *dev, struct clk *apb, struct clk *smi)
> >> > +{
> >> > +   int ret;
> >> > +
> >> > +   ret = pm_runtime_get_sync(dev);
> >> > +   if (ret < 0)
> >> > +           return ret;
> >> > +
> >> > +   ret = clk_prepare_enable(apb);
> >> > +   if (ret)
> >> > +           goto err_put_pm;
> >> > +
> >> > +   ret = clk_prepare_enable(smi);
> >> > +   if (ret)
> >> > +           goto err_disable_apb;
> >> > +
> >> > +   return 0;
> >> > +
> >> > +err_disable_apb:
> >> > +   clk_disable_unprepare(apb);
> >> > +err_put_pm:
> >> > +   pm_runtime_put_sync(dev);
> >> > +   return ret;
> >> > +}
> >> > +
> >> > +static void
> >> > +mtk_smi_disable(struct device *dev, struct clk *apb, struct clk *smi)
> >> > +{
> >> > +   clk_disable_unprepare(smi);
> >> > +   clk_disable_unprepare(apb);
> >> > +   pm_runtime_put_sync(dev);
> >> > +}
> >> > +
> >> > +static int mtk_smi_common_enable(struct mtk_smi_common *common)
> >> > +{
> >> > +   return mtk_smi_enable(common->dev, common->clk_apb, common->clk_smi);
> >> > +}
> >> > +
> >> > +static void mtk_smi_common_disable(struct mtk_smi_common *common)
> >> > +{
> >> > +   mtk_smi_disable(common->dev, common->clk_apb, common->clk_smi);
> >> > +}
> >> > +
> >> > +static int mtk_smi_larb_enable(struct mtk_smi_larb *larb)
> >> > +{
> >> > +   return mtk_smi_enable(larb->dev, larb->clk_apb, larb->clk_smi);
> >> > +}
> >> > +
> >> > +static void mtk_smi_larb_disable(struct mtk_smi_larb *larb)
> >> > +{
> >> > +   mtk_smi_disable(larb->dev, larb->clk_apb, larb->clk_smi);
> >> > +}
> >> > +
> >>
> >> This is somehow over-engineered. Just use mtk_smi_enable and mtk_smi_disable
> >> instead of adding an extra indirection.
> >
> > I added this only for readable...then the code in mtk_smi_larb_get below
> > may looks simple and readable.
> >
> > If I use mtk_smi_enable/disable directly, the code will be like our
> > v5[1], is it OK?
> > Maybe I don't need these help function here, and only add more comment
> > based on v5.
> >
> > [1]
> > http://lists.linuxfoundation.org/pipermail/iommu/2015-October/014590.html
> 
> bike-shedding...
> 
> I like the fact that Yong is trying to make his helpers more type-safe.
> But, perhaps we can rename "struct mtk_smi_common" as "struct
> mtk_smi", and then make "struct mtk_smi_larb" contain a "struct
> mtk_smi":
> 
> struct mtk_smi {
>   struct device *dev;
>   struct clk *clk_apb, *clk_smi;
> }
> 
> struct mtk_smi_larb {
>   struct mtk_smi;
>   ...
> }
> 
> 
> Then, have:
> 
> int mtk_smi_enable(struct mtk_smi *smi)
> {
>   clk_enable(smi->clk_apb);
>   ...
> }
> 
> int mtk_smi_disable(struct mtk_smi *smi)
> {
> }
> 
> int mtk_smi_larb_get(struct device *larbdev)
> {
>   struct mtk_smi_larb *larb = dev_get_drvdata(larbdev);
>   struct mtk_smi *common = dev_get_drvdata(larb->smi_common_dev);
> 
>   mtk_smi_enable(common);
>   mtk_smi_enable(&larb->smi);
>   ...
> }

Thanks. I will change like this in next time.

> 
> >>
> >> > +int mtk_smi_larb_get(struct device *larbdev)
> >> > +{
> >> > +   struct mtk_smi_larb *larb = dev_get_drvdata(larbdev);
> >> > +   struct mtk_smi_common *common = dev_get_drvdata(larb->smi_common_dev);
> >> > +   int ret;
> >> > +
> >> > +   ret = mtk_smi_common_enable(common);
> >> > +   if (ret)
> >> > +           return ret;
> >> > +
> >> > +   ret = mtk_smi_larb_enable(larb);
> >> > +   if (ret)
> >> > +           goto err_put_smi;
> >> > +
> >> > +   /* Configure the iommu info */
> >> > +   writel_relaxed(larb->mmu, larb->base + SMI_LARB_MMU_EN);
> 
> I think this should probably be writel() not writel_relaxed, since you
> really do want the barrier to ensure all other register accesses have
> completed before enabling the MMU.

Yes. I will fix this.

> 
> >> > +
> >> > +   return 0;
> >> > +
> >> > +err_put_smi:
> >> > +   mtk_smi_common_disable(common);
> >> > +   return ret;
> >> > +}
> >> > +
> >> > +void mtk_smi_larb_put(struct device *larbdev)
> >> > +{
> >> > +   struct mtk_smi_larb *larb = dev_get_drvdata(larbdev);
> >> > +   struct mtk_smi_common *common = dev_get_drvdata(larb->smi_common_dev);
> >> > +
> >> > +   writel_relaxed(0, larb->base + SMI_LARB_MMU_EN);
> >> > +   mtk_smi_larb_disable(larb);
> >> > +   mtk_smi_common_disable(common);
> >> > +}
> >> > +
> >>
> >> Looks strange that you just disable all MMUs while you only enable some of
> >> them at runtime. Unfortunately the datasheet I have lacks the SMI part, so I
> >> can just guess how the HW is working.
> >> From the DTS it looks like as if a larb can be used by two different
> >> components (e.g. larb0 from ovl0 and rdma0). Wouldn't that produce a conflict?
> >
> > Thanks. It's really a problem.
> >
> > There are OVL0 and MDP in larb0, Both will call mtk_smi_larb_get/put, we
> > cann't disable all the MMUs in whole the larb0 here.  This register
> > should be reset to zero while the larb power domain turning off(rely on
> > the power-domain ref count).
> > I will delete this(keep this in our V5.)
> 
> Hmm, mtk_smi_config_port(.., false) clears the bit in larb->mmu, but
> does not actually "disable" an enabled mmu.

Actually mtk_smi_config_port(.., false) will never be called currently.

If anybody would like to call iommu_detach_device to config-port false.
He will get the log below since the current iommu core don't support
detach one device in a iommu-group which have many devices.

That's to say that the larb->mmu is initialized in probe, and will never
be changed again.

(151119_13:39:37.472)WARNING:
at /proj/mtk40525/upstreamdev/v4.4/kernel/mediatek/drivers/iommu/iommu.c:1154
(151119_13:39:37.472)Modules linked in:
(151119_13:39:37.472)CPU: 1 PID: 731 Comm: sh Not tainted 4.4.0-rc1+ #37
(151119_13:39:37.472)Hardware name: MediaTek MT8173 evaluation board
(DT)
(151119_13:39:37.472)task: ffffffc076bb4d00 ti: ffffffc076bdc000
task.ti: ffffffc076bdc000
(151119_13:39:37.472)PC is at iommu_detach_device+0x5c/0xb0
(151119_13:39:37.472)LR is at iommu_detach_device+0x30/0xb0
...
(151119_13:39:37.550)---[ end trace d831cba9f811edf3 ]---
(151119_13:39:37.550)Call trace:
(151119_13:39:37.550)[<ffffffc0003f8c70>] iommu_detach_device+0x5c/0xb0

By the way, In the next version I plan to delete this interface
mtk_smi_config_port, use the additional data of the component-bind
instead of this.

> The MMU will be disabled only on the next mtk_smi_larb_get() (for a
> different port on the same larb).
> I guess this is ok.  The only weird thing is this situation, where an
> MMU can be left enabled when its user is done with it:
> 
>  /* configure port 0 as 'enabled' */
>  mtk_smi_config_port(0, true);
>  /* configure port 1 as 'enabled' */
>  mtk_smi_config_port(1, true);
> 
> /* user of port 0 wants to do work */
> mtk_smi_larb_get() /* turns on all clks, power & enables both MMUs */
> 
> /* user of port 1 wants to do work */
> mtk_smi_larb_get()
> 
> /* user of port 1 done doing work */
> mtk_smi_larb_put()
> 
> /* MMU 1 is still enabled */

This is really not so perfect in this case.

Even though the iommu-core support iommu-detach dynamically for our case
in the future(there is no plan currently), This don't have bad effect.

If user of port 1 want to work again, He should call mtk_smi_larb_get
again.

>From the HW, there may be different modules in a local arbiter, SMI here
can not detect which module call mtk_smi_larb_put and disable his
special iommu bits. After all mtk_smi_larb_put is mainly for power off
and disable the clocks.

> 
> 
> Thanks!
> -Dan


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