linux-kernel - Re:Re: [PATCH] powerpc/Kconfig: Make FSL_85XX_CACHE

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Message-ID: <AFEA1QBVCHZojVUNOs1Cfqrs.3.1579588704764.Hmail.wenhu.wang@vivo.com>
Date:   Tue, 21 Jan 2020 14:38:24 +0800 (GMT+08:00)
From:   王文虎 <wenhu.wang@...o.com>
To:     Scott Wood <oss@...error.net>
Cc:     wangwenhu <wenhu.pku@...il.com>,
        Kumar Gala <galak@...nel.crashing.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        trivial@...nel.org, Rai Harninder <harninder.rai@....com>
Subject: Re:Re: [PATCH] powerpc/Kconfig: Make FSL_85XX_CACHE_SRAM configurable

发件人：Scott Wood <oss@...error.net>
发送日期：2020-01-21 13:49:59
收件人："王文虎" <wenhu.wang@...o.com>
抄送人：wangwenhu <wenhu.pku@...il.com>,Kumar Gala <galak@...nel.crashing.org>,Benjamin Herrenschmidt <benh@...nel.crashing.org>,Paul Mackerras <paulus@...ba.org>,Michael Ellerman <mpe@...erman.id.au>,linuxppc-dev@...ts.ozlabs.org,linux-kernel@...r.kernel.org,trivial@...nel.org,Rai Harninder <harninder.rai@....com>
主题：Re: [PATCH] powerpc/Kconfig: Make FSL_85XX_CACHE_SRAM configurable>On Tue, 2020-01-21 at 13:20 +0800, 王文虎 wrote:
>> From: Scott Wood <oss@...error.net>
>> Date: 2020-01-21 11:25:25
>> To:  wangwenhu <wenhu.pku@...il.com>,Kumar Gala <galak@...nel.crashing.org>,
>> Benjamin Herrenschmidt <benh@...nel.crashing.org>,Paul Mackerras <
>> paulus@...ba.org>,Michael Ellerman <mpe@...erman.id.au>,
>> linuxppc-dev@...ts.ozlabs.org,linux-kernel@...r.kernel.org
>> Cc:  trivial@...nel.org,wenhu.wang@...o.com,Rai Harninder <
>> harninder.rai@....com>
>> Subject: Re: [PATCH] powerpc/Kconfig: Make FSL_85XX_CACHE_SRAM
>> configurable>On Mon, 2020-01-20 at 06:43 -0800, wangwenhu wrote:
>> > > From: wangwenhu <wenhu.wang@...o.com>
>> > > 
>> > > When generating .config file with menuconfig on Freescale BOOKE
>> > > SOC, FSL_85XX_CACHE_SRAM is not configurable for the lack of
>> > > description in the Kconfig field, which makes it impossible
>> > > to support L2Cache-Sram driver. Add a description to make it
>> > > configurable.
>> > > 
>> > > Signed-off-by: wangwenhu <wenhu.wang@...o.com>
>> > 
>> > The intent was that drivers using the SRAM API would select the
>> > symbol.  What
>> > is the use case for selecting it manually?
>> > 
>> 
>> With a repository of multiple products(meaning different defconfigs) and
>> multiple
>> developers, the Kconfigs of the Kernel Source Tree change frequently. So the
>> "make menuconfig"
>> process is needed for defconfigs' re-generating or updating for the
>> complexity of dependencies
>> between different features defined in the Kconfigs.
>
>That doesn't answer my question of how the SRAM code would be useful other
>than to some other driver that uses the API (which would use "select").  There
>is no userspace API.  You could use the kernel command line to configure the
>SRAM but you need to get the address of it for it to be useful.
>

Like you've asked below, via /dev/mem or direct calling within the Kernel.
And they are not submitted yes, under development.

>> > Since this code was added almost ten years ago and there are still no (in-
>> > tree?) users of the API, we should just remove the sram code (unless this
>> > prods someone to submit such a user very soon).
>> > 
>> 
>> Yes, pretty long a time. But we DO really use the API now for
>> PPCE500/Freescale SoC.
>
>I do not see any users in the kernel tree.  Are you talking about out-of-tree
>code, or something that you've submitted or will submit soon?  Or are you
>accessing it via /dev/mem?
>

Both, but not submitted yet, and partly under development.

>> Like sometimes we need to reset the whole RAM, then the L2-Cache would be
>> used as
>> SRAM for backup using. Since it is useful for us now, a re-consideration is
>> recommanded.
>
>Where is the code that would do this?
>

Currently under development, and not submitted yet.

>-Scott
>> 
>

Wenhu