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

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Date:   Sat, 29 Feb 2020 17:12:58 -0600
From:   Scott Wood <oss@...error.net>
To:     王文虎 <wenhu.wang@...o.com>
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

On Tue, 2020-01-21 at 14:38 +0800, 王文虎 wrote:
> 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>,B
> enjamin 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.

If they are calling within the kernel, then whatever driver that is should
select FSL_85XX_CACHE_SRAM.  Directly accessing /dev/mem without any way for
the kernel to advertise where it is or which parts of SRAM are available for
use sounds like a bad idea.

-Scott