Re: [PATCH 3/3] clk: qcom: add MSM8x60 MMCC driver

[Konrad Dybcio]

On 5/30/26 3:58 PM, Herman van Hazendonk wrote:
> Add a clock driver for the Multimedia Clock Controller (MMCC) on the
> MSM8x60 family (MSM8260/MSM8660/APQ8060) - the Scorpion-class
> generation that preceded MSM8960's Krait CPUs.
> 
> The MMCC layout on MSM8x60 differs from MSM8960 in several ways that
> make a separate driver cleaner than parameterising mmcc-msm8960.c:
> 
>   - the pix_rdi mux requires a custom set_parent op that temporarily
>     enables both parents during the glitch-free transition;
>   - the IJPEG GDSC requires releasing AXI, AHB and CORE resets;
>   - several rate-source pairs (MDP pixel, GFX2D/3D) only exist on
>     8x60 (e.g. PLL2-derived 228571000/266667000 for graphics);
>   - the camera CSI / VFE / JPEG / VPE / ROT clock topology lacks the
>     later 8960 reorganisation.
> 
> Used on the HP TouchPad (Tenderloin) for graphics (Adreno A220),
> display (MDP4), camera (CSI/VFE), JPEG (Gemini), VIDC, VPE and
> rotator. Reset IDs are exposed via a separate header so consumers
> can reset the GDSCs and individual blocks.
> 
> Signed-off-by: Herman van Hazendonk <github.com@xxxxxxxxxx>
> ---

[...]

> +	.clkr.hw.init = &(struct clk_init_data){
> +		.name = "pll2",
> +		.parent_data = (const struct clk_parent_data[]){
> +			{ .fw_name = "pxo", .name = "pxo_board" },

Please drop .name (the kernel-global clock lookup), this is only a
backwards compatiblity measure on existing drivers. For new entries,
.index is the best (because well, it's the fastest)

[...]

> +static struct clk_branch camclk0_clk = {
> +	.halt_reg = 0x01e8,
> +	.halt_bit = 15,
> +	/*
> +	 * The legacy webOS kernel used halt_reg = NULL for this clock,
> +	 * meaning it never checked the halt status. The hardware doesn't
> +	 * properly report the clock state via the halt register. Use
> +	 * BRANCH_HALT_SKIP to avoid the "status stuck at 'off'" warning.

It may be that some piece of hw is holding this clock online behind the
scenes. Is there perhaps a Qualcomm-authored commit that mentions the hw
bug, or is it a guess? Due to the age of this chip I would imagine I
won't be find an answer if you don't have one..

[...]

I see you have a lot of inline note-to-self comments, please strip some
of them.

Konrad