linux-kernel - Re: [PATCH RESEND] clk: vc5: fix output disabling when enabling a FOD

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Message-ID: <162320001952.1835121.12525475382527041110@swboyd.mtv.corp.google.com>
Date:   Tue, 08 Jun 2021 17:53:39 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Luca Ceresoli <luca@...aceresoli.net>, linux-clk@...r.kernel.org
Cc:     Luca Ceresoli <luca@...aceresoli.net>,
        Michael Turquette <mturquette@...libre.com>,
        linux-kernel@...r.kernel.org, Adam Ford <aford173@...il.com>
Subject: Re: [PATCH RESEND] clk: vc5: fix output disabling when enabling a FOD

Quoting Luca Ceresoli (2021-05-27 14:16:47)
> On 5P49V6965, when an output is enabled we enable the corresponding
> FOD. When this happens for the first time, and specifically when writing
> register VC5_OUT_DIV_CONTROL in vc5_clk_out_prepare(), all other outputs
> are stopped for a short time and then restarted.
> 
> According to Renesas support this is intended: "The reason for that is VC6E
> has synced up all output function".
> 
> This behaviour can be disabled at least on VersaClock 6E devices, of which
> only the 5P49V6965 is currently implemented by this driver. This requires
> writing bit 7 (bypass_sync{1..4}) in register 0x20..0x50.  Those registers
> are named "Unused Factory Reserved Register", and the bits are documented
> as "Skip VDDO<N> verification", which does not clearly explain the relation
> to FOD sync. However according to Renesas support as well as my testing
> setting this bit does prevent disabling of all clock outputs when enabling
> a FOD.
> 
> See "VersaClock ® 6E Family Register Descriptions and Programming Guide"
> (August 30, 2018), Table 116 "Power Up VDD check", page 58:
> https://www.renesas.com/us/en/document/mau/versaclock-6e-family-register-descriptions-and-programming-guide
> 
> Signed-off-by: Luca Ceresoli <luca@...aceresoli.net>
> Reviewed-by: Adam Ford <aford173@...il.com>
> 
> ---

Applied to clk-next