linux-kernel - Re: [PATCH v4] remoteproc: mediatek: Fix side effect of mt8195 sram power on

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Message-ID: <20220317162509.GA2630429@p14s>
Date:   Thu, 17 Mar 2022 10:25:09 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     Tinghan Shen <tinghan.shen@...iatek.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-remoteproc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH v4] remoteproc: mediatek: Fix side effect of mt8195 sram
 power on

On Wed, Mar 16, 2022 at 05:44:04PM +0100, AngeloGioacchino Del Regno wrote:
> Il 16/03/22 17:34, Mathieu Poirier ha scritto:
> > Good morning,
> > 
> > On Wed, Mar 16, 2022 at 11:11:17AM +0800, Tinghan Shen wrote:
> > > The definition of L1TCM_SRAM_PDN bits on mt8195 is different to mt8192.
> > > 
> > > L1TCM_SRAM_PDN bits[3:0] control the power of mt8195 L1TCM SRAM.
> > > 
> > > L1TCM_SRAM_PDN bits[7:4] control the access path to EMI for SCP.
> > > These bits have to be powered on to allow EMI access for SCP.
> > > 
> > > Bits[7:4] also affect audio DSP because audio DSP and SCP are
> > > placed on the same hardware bus. If SCP cannot access EMI, audio DSP is
> > > blocked too.
> > > 
> > > L1TCM_SRAM_PDN bits[31:8] are not used.
> > > 
> > > This fix removes modification of bits[7:4] when power on/off mt8195 SCP
> > > L1TCM. It's because the modification introduces a short period of time
> > > blocking audio DSP to access EMI. This was not a problem until we have
> > > to load both SCP module and audio DSP module. audio DSP needs to access
> > > EMI because it has source/data on DRAM. Audio DSP will have unexpected
> > > behavior when it accesses EMI and the SCP driver blocks the EMI path at
> > > the same time.
> > > 
> > > Fixes: 79111df414fc ("remoteproc: mediatek: Support mt8195 scp")
> > > Signed-off-by: Tinghan Shen <tinghan.shen@...iatek.com>
> > > Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> > > Reviewed-by: Matthias Brugger <matthias.bgg@...il.com>
> > > ---
> > > v4: add Fixes and Reviewed-by tags
> > > v3: fix build error
> > > v2: apply comments about macro definition and function calls
> > > ---
> > >   drivers/remoteproc/mtk_common.h |  2 ++
> > >   drivers/remoteproc/mtk_scp.c    | 67 +++++++++++++++++++++++++++++++----------
> > >   2 files changed, 53 insertions(+), 16 deletions(-)
> > > 
> > > diff --git a/drivers/remoteproc/mtk_common.h b/drivers/remoteproc/mtk_common.h
> > > index 5ff3867c72f3..ff954a06637c 100644
> > > --- a/drivers/remoteproc/mtk_common.h
> > > +++ b/drivers/remoteproc/mtk_common.h
> > > @@ -51,6 +51,8 @@
> > >   #define MT8192_CORE0_WDT_IRQ		0x10030
> > >   #define MT8192_CORE0_WDT_CFG		0x10034
> > > +#define MT8195_L1TCM_SRAM_PDN_RESERVED_RSI_BITS		GENMASK(7, 4)
> > > +
> > >   #define SCP_FW_VER_LEN			32
> > >   #define SCP_SHARE_BUFFER_SIZE		288
> > > diff --git a/drivers/remoteproc/mtk_scp.c b/drivers/remoteproc/mtk_scp.c
> > > index 36e48cf58ed6..5f686fe09203 100644
> > > --- a/drivers/remoteproc/mtk_scp.c
> > > +++ b/drivers/remoteproc/mtk_scp.c
> > > @@ -365,22 +365,22 @@ static int mt8183_scp_before_load(struct mtk_scp *scp)
> > >   	return 0;
> > >   }
> > > -static void mt8192_power_on_sram(void __iomem *addr)
> > > +static void scp_sram_power_on(void __iomem *addr, u32 reserved_mask)
> > 
> > Why is @reserved_mask needed?  It is not described in the changelong and as far
> > as I can see in this patchset the parameter is always set to '0', which has no
> > effect on the mask that gets generated.
> > 
> 
> Hello Mathieu,
> the @reserved_mask is explained in perhaps not very very clear terms, meaning
> that he's not explicitly saying the name of the new param, but that's it:
> 
> "This fix removes modification of bits[7:4] when power on/off mt8195 SCP
> L1TCM."
> 
> ....and it's actually being used, check below....
> 
> > Thanks,
> > Mathieu
> > 
> > >   {
> > >   	int i;
> > >   	for (i = 31; i >= 0; i--)
> > > -		writel(GENMASK(i, 0), addr);
> > > +		writel(GENMASK(i, 0) & ~reserved_mask, addr);
> > >   	writel(0, addr);
> > >   }
> > > -static void mt8192_power_off_sram(void __iomem *addr)
> > > +static void scp_sram_power_off(void __iomem *addr, u32 reserved_mask)
> 
> ...snip...
> 
> > > +static int mt8195_scp_before_load(struct mtk_scp *scp)
> > > +{
> > > +	/* clear SPM interrupt, SCP2SPM_IPC_CLR */
> > > +	writel(0xff, scp->reg_base + MT8192_SCP2SPM_IPC_CLR);
> > > +
> > > +	writel(1, scp->reg_base + MT8192_CORE0_SW_RSTN_SET);
> > > +
> > > +	/* enable SRAM clock */
> > > +	scp_sram_power_on(scp->reg_base + MT8192_L2TCM_SRAM_PD_0, 0);
> > > +	scp_sram_power_on(scp->reg_base + MT8192_L2TCM_SRAM_PD_1, 0);
> > > +	scp_sram_power_on(scp->reg_base + MT8192_L2TCM_SRAM_PD_2, 0);
> 
> 
> > > +	scp_sram_power_on(scp->reg_base + MT8192_L1TCM_SRAM_PDN,
> > > +			  MT8195_L1TCM_SRAM_PDN_RESERVED_RSI_BITS);
> 
> here	

Yes - it's obvious now that you point it out.  

This patch conflicts with the newly added support for mt8186[1].  I tried to fix
it but did not know if mt8185 needed the same kind of bit masking as mt8195.
Please have a look and rebase to rproc-next.

Thanks,
Mathieu

[1]. 80d691854ffb remoteproc: mediatek: Support mt8186 scp

> 
> > > +	scp_sram_power_on(scp->reg_base + MT8192_CPU0_SRAM_PD, 0);
> > >   	/* enable MPU for all memory regions */
> > >   	writel(0xff, scp->reg_base + MT8192_CORE0_MEM_ATT_PREDEF);
> 
> ...snip...
> 
> > > +
> > > +static void mt8195_scp_stop(struct mtk_scp *scp)
> > > +{
> > > +	/* Disable SRAM clock */
> > > +	scp_sram_power_off(scp->reg_base + MT8192_L2TCM_SRAM_PD_0, 0);
> > > +	scp_sram_power_off(scp->reg_base + MT8192_L2TCM_SRAM_PD_1, 0);
> > > +	scp_sram_power_off(scp->reg_base + MT8192_L2TCM_SRAM_PD_2, 0);
> > > +	scp_sram_power_off(scp->reg_base + MT8192_L1TCM_SRAM_PDN,
> > > +			   MT8195_L1TCM_SRAM_PDN_RESERVED_RSI_BITS);
> 
> and here 			^^^^^^^^
> 
> > > +	scp_sram_power_off(scp->reg_base + MT8192_CPU0_SRAM_PD, 0);
> 
> Cheers,
> Angelo