linux-kernel - Re: [PATCH] clk: sunxi-ng: h3/h5: Model H3 CLK

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Date:   Thu, 05 Jan 2023 18:30:21 +0100
From:   Jernej Škrabec <jernej.skrabec@...il.com>
To:     Chen-Yu Tsai <wens@...e.org>, Samuel Holland <samuel@...lland.org>
Cc:     Samuel Holland <samuel@...lland.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH] clk: sunxi-ng: h3/h5: Model H3 CLK_DRAM as a fixed clock

Dne četrtek, 29. december 2022 ob 05:22:30 CET je Samuel Holland napisal(a):
> The DRAM controller clock is only allowed to change frequency while the
> DRAM chips are in self-refresh. To support this, changes to the CLK_DRAM
> mux and divider have no effect until acknowledged by the memory dynamic
> frequency scaling (MDFS) hardware inside the DRAM controller. (There is
> a SDRCLK_UPD bit in DRAM_CFG_REG which should serve a similar purpose,
> but this bit actually does nothing.)
> 
> However, the MDFS hardware in H3 appears to be broken. Triggering a
> frequency change using the procedure from similar SoCs (A64/H5) hangs
> the hardware. Additionally, the vendor BSP specifically avoids using the
> MDFS hardware on H3, instead performing all DRAM PHY parameter updates
> and resets in software.
> 
> Thus, it is effectively impossible to change the CLK_DRAM mux/divider,
> so those features should not be modeled. Add CLK_SET_RATE_PARENT so
> frequency changes apply to PLL_DDR instead.
> 
> Signed-off-by: Samuel Holland <samuel@...lland.org>

Reviewed-by: Jernej Skrabec <jernej.skrabec@...il.com>

Best regards,
Jernej