linux-kernel - Re: [PATCH v3 2/3] soc: qcom: ubwc: Get HBB from SMEM

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Message-ID: <b2pqfrs2ptaoxxeanzumxyibmydsoiqslcsg6yrm4hihynowj4@mzazqnrptnyf>
Date: Thu, 8 Jan 2026 11:49:54 -0600
From: Bjorn Andersson <andersson@...nel.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Konrad Dybcio <konradybcio@...nel.org>, Kees Cook <kees@...nel.org>, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>, Rob Clark <robin.clark@....qualcomm.com>, 
	Sean Paul <sean@...rly.run>, Akhil P Oommen <akhilpo@....qualcomm.com>, 
	Dmitry Baryshkov <lumag@...nel.org>, Abhinav Kumar <abhinav.kumar@...ux.dev>, 
	Jessica Zhang <jesszhan0024@...il.com>, Marijn Suijten <marijn.suijten@...ainline.org>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, linux-kernel@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org, linux-hardening@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
	freedreno@...ts.freedesktop.org, Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH v3 2/3] soc: qcom: ubwc: Get HBB from SMEM

On Thu, Jan 08, 2026 at 04:45:49PM +0200, Dmitry Baryshkov wrote:
> On Thu, Jan 08, 2026 at 03:21:51PM +0100, Konrad Dybcio wrote:
> > From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
> > 
> > To make sure the correct settings for a given DRAM configuration get
> > applied, attempt to retrieve that data from SMEM (which happens to be
> > what the BSP kernel does, albeit with through convoluted means of the
> > bootloader altering the DT with this data).
> > 
> > Signed-off-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
> > 
> > ---
> > I'm not sure about this approach - perhaps a global variable storing
> > the selected config, which would then be non-const would be better?
> 
> I'd prefer if const data was const, split HBB to a separate API.
> 

I agree, but I'd prefer to avoid a separate API for it.

Instead I'd like to either return the struct by value (after updating
the hbb), but we then loose the ability to return errors, or by changing
the signature to:

int qcom_ubwc_config_get_data(struct qcom_ubwc_cfg_data *data)

This costs us an additional 16 bytes in each client (as the pointer is
replaced with the data), but I think it's a cleaner API.

Regards,
Bjorn