Re: [PATCH] remoteproc: mediatek: enable cache for mt8186 SCP

[allen-kh.cheng <allen-kh.cheng@mediatek.com>]

Hi Mathieu,

On Thu, 2022-03-24 at 09:56 -0600, Mathieu Poirier wrote:
> Hi Allen,
> 
> On Tue, Mar 22, 2022 at 08:28:45PM +0800, Allen-KH Cheng wrote:
> > 1. Set SCP cache size before loading SCP FW. (8KB+8KB)
> > 2. Adjust ipi_buf_offset from 0x7bdb0 to 0x3BDB0 for enableing
> > cache
> > 
> > SCP side
> >  - IPI Buffer: 0x3BDB0 <-> 0x3C000
> >  - Cache: 0x3C000 <-> 0x40000
> > 
> 
> I would also like to find in this changelog "why" this patch is
> needed and more
> importantly, how it remains compatible with existing
> implementation.  I am
> mostly worried about implemenations where the application processor
> is using
> caches while the SCP is not.
> 
> I will also need a couple of "Tested-by" tags before moving forward
> with this
> patch.
> 
> Thanks,
> Mathieu
> 

Sorry for the confusion.

This patch is for enableing cache in SCP.

In mt8186 SCP, we don't have enough SRAM so SCP will use DRAM as
execution space. 

The DRAM power and latency is much larger than SRAM, so cache is used
to slight these affects.

The cache support is designed in SCP bus Architecture.

We reserve 0x3C000 <-> 0x40000 in SRAM(SCP) to support cache and set
I-cache and D-cache size before loading SCP FW.

If there isn't no this patch, SCP is still working and would not
support cache when using DRAM.

This patch will not affect implemenations where the application
processor is using caches.

I will add more information in commit message for this PATCH
and Tested-by tags in next version.

Thanks,
Allen

> > Signed-off-by: Allen-KH Cheng <allen-kh.cheng@mediatek.com>
> > ---
> >  drivers/remoteproc/mtk_scp.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/remoteproc/mtk_scp.c
> > b/drivers/remoteproc/mtk_scp.c
> > index 38609153bf64..24065b6b4da8 100644
> > --- a/drivers/remoteproc/mtk_scp.c
> > +++ b/drivers/remoteproc/mtk_scp.c
> > @@ -401,6 +401,14 @@ static int mt8186_scp_before_load(struct
> > mtk_scp *scp)
> >  	writel(0x0, scp->reg_base + MT8186_SCP_L1_SRAM_PD_P1);
> >  	writel(0x0, scp->reg_base + MT8186_SCP_L1_SRAM_PD_p2);
> >  
> > +	/*
> > +	 * Set I-cache and D-cache size before loading SCP FW.
> > +	 * SCP SRAM logical address may change when cache size setting
> > differs.
> > +	 */
> > +	writel(MT8183_SCP_CACHE_CON_WAYEN | MT8183_SCP_CACHESIZE_8KB,
> > +	       scp->reg_base + MT8183_SCP_CACHE_CON);
> > +	writel(MT8183_SCP_CACHESIZE_8KB, scp->reg_base +
> > MT8183_SCP_DCACHE_CON);
> > +
> >  	return 0;
> >  }
> >  
> > @@ -905,7 +913,7 @@ static const struct mtk_scp_of_data
> > mt8186_of_data = {
> >  	.scp_da_to_va = mt8183_scp_da_to_va,
> >  	.host_to_scp_reg = MT8183_HOST_TO_SCP,
> >  	.host_to_scp_int_bit = MT8183_HOST_IPC_INT_BIT,
> > -	.ipi_buf_offset = 0x7bdb0,
> > +	.ipi_buf_offset = 0x3bdb0,
> >  };
> >  
> >  static const struct mtk_scp_of_data mt8192_of_data = {
> > -- 
> > 2.18.0
> > 


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