Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Chris Morgan <macroalpha82@gmail.com>
To:     andriy.shevchenko@linux.intel.com
Cc:     abel.vesa@nxp.com, festevam@gmail.com, heiko@sntech.de,
        kernel@pengutronix.de, lee.jones@linaro.org, lenb@kernel.org,
        linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-clk@vger.kernel.org, linux-imx@nxp.com,
        linux-kernel@vger.kernel.org, linux-rockchip@lists.infradead.org,
        mturquette@baylibre.com, rafael.j.wysocki@intel.com,
        rjw@rjwysocki.net, s.hauer@pengutronix.de, sboyd@kernel.org,
        shawnguo@kernel.org, zhangqing@rock-chips.com,
        Chris Morgan <macromorgan@hotmail.com>
Subject: Re: [PATCH v4 1/4] clk: fractional-divider: Export approximation algorithm to the CCF users
Date:   Tue,  7 Sep 2021 10:44:00 -0500
Message-Id: <20210907154400.26656-1-macroalpha82@gmail.com>
In-Reply-To: <20210812170025.67074-1-andriy.shevchenko@linux.intel.com>
References: <20210812170025.67074-1-andriy.shevchenko@linux.intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Chris Morgan <macromorgan@hotmail.com>

Unfortunately, I can confirm this breaks the DSI panel on the Rockchip
PX30 (and possibly other SoCs). Tested on my Odroid Go Advance. When
I revert 4e7cf74fa3b2 "clk: fractional-divider: Export approximation
algorithm to the CCF users" and 928f9e268611 "clk: fractional-divider:
Hide clk_fractional_divider_ops from wide audience" the panel begins
working again as expected on the master branch.

It looks like an assumption is made in the vop_crtc_mode_fixup()
function in the rockchip_drm_vop.c that gets broken with this change.
Specifically, the function says in the comments "When DRM gives us a
mode, we should add 999 Hz to it.". I believe this is no longer true
after this clk change, and when I remove the + 999 from the function
the DSI panel works again. Note that I do not know the implications
of removing this 999 aside from that it fixes the DSI panel on my
PX30 after this change, so I don't know if it's a positive change
or not.

Thank you.