clk: qcom: Allow constant ratio freq tables for rcg

BugLink: https://bugs.launchpad.net/bugs/1858462

[ Upstream commit efd164b5 ]

Some RCGs (the gfx_3d_src_clk in msm8998 for example) are basically just
some constant ratio from the input across the entire frequency range.  It
would be great if we could specify the frequency table as a single entry
constant ratio instead of a long list, ie:

	{ .src = P_GPUPLL0_OUT_EVEN, .pre_div = 3 },
        { }

So, lets support that.

We need to fix a corner case in qcom_find_freq() where if the freq table
is non-null, but has no frequencies, we end up returning an "entry" before
the table array, which is bad.  Then, we need ignore the freq from the
table, and instead base everything on the requested freq.
Suggested-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
Link: https://lkml.kernel.org/r/20191031185715.15504-1-jeffrey.l.hugo@gmail.comSigned-off-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/clk/qcom/clk-rcg2.c

@@ -196,6 +196,8 @@ static int _freq_tbl_determine_rate(struct clk_hw *hw,
 	p = clk_hw_get_parent_by_index(hw, index);
 	if (clk_flags & CLK_SET_RATE_PARENT) {
 		if (f->pre_div) {
+			if (!rate)
+				rate = req->rate;
 			rate /= 2;
 			rate *= f->pre_div + 1;
 		}

drivers/clk/qcom/common.c

@@ -36,6 +36,9 @@ struct freq_tbl *qcom_find_freq(const struct freq_tbl *f, unsigned long rate)
 	if (!f)
 		return NULL;
 
+	if (!f->freq)
+		return f;
+
 	for (; f->freq; f++)
 		if (rate <= f->freq)
 			return f;