linux-kernel - Re: [PATCH v3 4/4] drm/msm/dpu: fix SSPP_UBWC_STATIC

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Message-ID: <fnlkcpf4dfgcy4cshl6g3ibjoon7pvdxyvmejokqygfyc2b2v3@og2xzf6fzuhj>
Date: Mon, 19 Jan 2026 13:27:40 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jesszhan0024@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Konrad Dybcio <konradybcio@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        Stephan Gerhold <stephan.gerhold@...aro.org>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Val Packett <val@...kett.cool>
Subject: Re: [PATCH v3 4/4] drm/msm/dpu: fix SSPP_UBWC_STATIC_CTRL
 programming on UBWC 5.x+

On Mon, Jan 19, 2026 at 12:08:07PM +0100, Konrad Dybcio wrote:
> On 1/19/26 9:17 AM, Dmitry Baryshkov wrote:
> > Code in dpu_hw_sspp_setup_format() doesn't handle UBWC versions bigger
> > than 4.0. Replace switch-case with if-else checks, making sure that the
> > register is initialized on UBWC 5.x (and later) hosts.
> > 
> > Fixes: c2577fc1740d ("drm/msm/dpu: Add support for SM8750")
> > Tested-by: Val Packett <val@...kett.cool> # x1e80100-dell-latitude-7455
> > Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
> > ---
> >  drivers/gpu/drm/msm/disp/dpu1/dpu_hw_sspp.c | 44 +++++++++++++++--------------
> >  1 file changed, 23 insertions(+), 21 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_sspp.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_sspp.c
> > index a99e33230514..80a9fb76b139 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_sspp.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_sspp.c
> > @@ -279,6 +279,7 @@ static void dpu_hw_sspp_setup_format(struct dpu_sw_pipe *pipe,
> >  
> >  	if (fmt->fetch_mode != MDP_FETCH_LINEAR) {
> >  		u32 hbb = ctx->ubwc->highest_bank_bit - 13;
> > +		u32 ctrl_val;
> >  
> >  		if (MSM_FORMAT_IS_UBWC(fmt))
> >  			opmode |= MDSS_MDP_OP_BWC_EN;
> > @@ -286,30 +287,31 @@ static void dpu_hw_sspp_setup_format(struct dpu_sw_pipe *pipe,
> >  		DPU_REG_WRITE(c, SSPP_FETCH_CONFIG,
> >  			DPU_FETCH_CONFIG_RESET_VALUE |
> >  			hbb << 18);
> > -		switch (ctx->ubwc->ubwc_enc_version) {
> > -		case UBWC_1_0:
> > +
> > +		if (ctx->ubwc->ubwc_enc_version == UBWC_1_0) {
> >  			fast_clear = fmt->alpha_enable ? BIT(31) : 0;
> > -			DPU_REG_WRITE(c, ubwc_static_ctrl_off,
> > -					fast_clear | (ctx->ubwc->ubwc_swizzle & 0x1) |
> > -					BIT(8) |
> > -					(hbb << 4));
> > -			break;
> > -		case UBWC_2_0:
> > +			ctrl_val = fast_clear | (ctx->ubwc->ubwc_swizzle & 0x1) |
> > +				BIT(8) | (hbb << 4);
> > +		} else if (ctx->ubwc->ubwc_enc_version == UBWC_2_0) {
> >  			fast_clear = fmt->alpha_enable ? BIT(31) : 0;
> > -			DPU_REG_WRITE(c, ubwc_static_ctrl_off,
> > -					fast_clear | (ctx->ubwc->ubwc_swizzle) |
> > -					(hbb << 4));
> > -			break;
> > -		case UBWC_3_0:
> > -			DPU_REG_WRITE(c, ubwc_static_ctrl_off,
> > -					BIT(30) | (ctx->ubwc->ubwc_swizzle) |
> > -					(hbb << 4));
> > -			break;
> > -		case UBWC_4_0:
> > -			DPU_REG_WRITE(c, ubwc_static_ctrl_off,
> > -					MSM_FORMAT_IS_YUV(fmt) ? 0 : BIT(30));
> > -			break;
> > +			ctrl_val = fast_clear | ctx->ubwc->ubwc_swizzle | (hbb << 4);
> > +		} else if (ctx->ubwc->ubwc_enc_version == UBWC_3_0) {
> > +			ctrl_val = BIT(30) | (ctx->ubwc->ubwc_swizzle) | (hbb << 4);
> > +		} else if (ctx->ubwc->ubwc_enc_version == UBWC_4_0) {
> > +			ctrl_val = MSM_FORMAT_IS_YUV(fmt) ? 0 : BIT(30);
> > +		} else if (ctx->ubwc->ubwc_enc_version <= UBWC_6_0) {
> > +			if (MSM_FORMAT_IS_YUV(fmt))
> > +				ctrl_val = 0;
> > +			else if (MSM_FORMAT_IS_DX(fmt)) /* or FP16, but it's unsupported */
> > +				ctrl_val = BIT(30);
> > +			else
> > +				ctrl_val = BIT(30) | BIT(31);
> 
> Can we name these magic bits?

I will raise the question internally. In general, I'd like to start
shifting towards generated reg descriptions, but it will take some time
to implement.

> 
> There's 2 more bitfields that I see downstream sets here (but it
> doesn't claim to support UBWC6).. 

For the formats which we don't support upstream. I'll add a comment
here (and I probably should send another iteration anyway, fixing the
error register too).

-- 
With best wishes
Dmitry