linux-kernel - Re: [PATCH] soc: qcom: llcc: Fix dis_cap_alloc and retain_on

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Message-ID: <20231106230103.GA3553829@hu-bjorande-lv.qualcomm.com>
Date:   Mon, 6 Nov 2023 15:01:03 -0800
From:   Bjorn Andersson <quic_bjorande@...cinc.com>
To:     Mukesh Ojha <quic_mojha@...cinc.com>
CC:     Atul Dhudase <quic_adhudase@...cinc.com>, <agross@...nel.org>,
        <andersson@...nel.org>, <konrad.dybcio@...aro.org>,
        <swboyd@...omium.org>, <isaacm@...eaurora.org>,
        <dianders@...omium.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] soc: qcom: llcc: Fix dis_cap_alloc and retain_on_pc
 configuration

On Mon, Nov 06, 2023 at 12:24:28PM +0530, Mukesh Ojha wrote:
> 
> 
> On 11/4/2023 1:03 AM, Bjorn Andersson wrote:
> > On Fri, Nov 03, 2023 at 04:27:12PM +0530, Atul Dhudase wrote:
> > > While programming dis_cap_alloc and retain_on_pc, set a bit
> > > corresponding to a specific SCID without disturbing the
> > > previously configured bits.
> > > 
> > 
> > As far as I can see, the only invocation of _qcom_llcc_cfg_program()
> > comes from qcom_llcc_cfg_program(), which is only called once, from
> > qcom_llcc_probe(), and here also seems to only be the single write to
> > these two registers.
> 
> It does not look to be single write but the write is for each slice
> in the same register which was overriding other slices values.
> 

Ahh, you're right. I missed that it was hitting the same register in
each iteration.

My concern remains though, unless a platform defines 32 slices only a
subset of the bits in the two registers will be touched - leaving the
remaining bits in whatever state they happened to have.

Regards,
Bjorn

> -Mukesh
> > 
> > This implies that "the previously configured bits" would be some unknown
> > configuration provided to us either from the bootloader or by reset of
> > the hardware. As such this changes the value of the two registers from
> > being known, to having 31 unknown bits.
> > 
> > 
> > I'm not saying that the change is wrong, but you're altering the
> > behavior of every platform except SDM845.
> > As such, I want the commit message to provide an actual problem
> > description, and mention the fact that you're changing the logic to
> > retain the state prior to Linux.
> > 
> > Regards,
> > Bjorn
> > 
> > > Fixes: c14e64b46944 ("soc: qcom: llcc: Support chipsets that can write to llcc")
> > > Signed-off-by: Atul Dhudase <quic_adhudase@...cinc.com>
> > > ---
> > >   drivers/soc/qcom/llcc-qcom.c | 8 ++++----
> > >   1 file changed, 4 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/soc/qcom/llcc-qcom.c b/drivers/soc/qcom/llcc-qcom.c
> > > index 674abd0d6700..509d972c1bd9 100644
> > > --- a/drivers/soc/qcom/llcc-qcom.c
> > > +++ b/drivers/soc/qcom/llcc-qcom.c
> > > @@ -941,15 +941,15 @@ static int _qcom_llcc_cfg_program(const struct llcc_slice_config *config,
> > >   		u32 disable_cap_alloc, retain_pc;
> > > 
> > >   		disable_cap_alloc = config->dis_cap_alloc << config->slice_id;
> > > -		ret = regmap_write(drv_data->bcast_regmap,
> > > -				LLCC_TRP_SCID_DIS_CAP_ALLOC, disable_cap_alloc);
> > > +		ret = regmap_update_bits(drv_data->bcast_regmap, LLCC_TRP_SCID_DIS_CAP_ALLOC,
> > > +				BIT(config->slice_id), disable_cap_alloc);
> > >   		if (ret)
> > >   			return ret;
> > > 
> > >   		if (drv_data->version < LLCC_VERSION_4_1_0_0) {
> > >   			retain_pc = config->retain_on_pc << config->slice_id;
> > > -			ret = regmap_write(drv_data->bcast_regmap,
> > > -					LLCC_TRP_PCB_ACT, retain_pc);
> > > +			ret = regmap_update_bits(drv_data->bcast_regmap, LLCC_TRP_PCB_ACT,
> > > +					BIT(config->slice_id), retain_pc);
> > >   			if (ret)
> > >   				return ret;
> > >   		}
> > > --
> > > 2.25.1
> > >