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Commit 4a2c4d1a authored by Douglas Anderson's avatar Douglas Anderson Committed by Greg Kroah-Hartman
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soc: qcom: geni: geni_se_clk_freq_match() should always accept multiples 

[ Upstream commit 867d4aa7013fdee8b962cde1711f96c8dd86d926 ]

The geni_se_clk_freq_match() has some strange semantics.  Specifically
it is defined with two modes:
1. It can find a clock that's an exact multiple of the requested rate
2. It can find a non-exact match but it can't handle multiples then

...but callers should always be able to handle a clock that is a
multiple of the requested clock so mode #2 doesn't really make sense.
Let's change the semantics so that the non-exact match can also accept
multiples and then change the code to handle that.

The only caller of this code is the unlanded SPI driver [1] which
currently passes "exact = True", thus it should be safe to change the
semantics in this way.  ...and, in fact, the SPI driver should likely
be modified to pass "exact = False" (with the new semantics) since
that will allow it to work with SPI devices that request a clock rate
that doesn't exactly match a rate we can make.

[1] https://lkml.kernel.org/r/1535107336-2214-1-git-send-email-dkota@codeaurora.org



Fixes: eddac5af ("soc: qcom: Add GENI based QUP Wrapper driver")
Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
Reviewed-by: default avatarMatthias Kaehlcke <mka@chromium.org>
Signed-off-by: default avatarAndy Gross <andy.gross@linaro.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 331ed266

drivers/soc/qcom/qcom-geni-se.c

+22 −15
Original line number Diff line number Diff line
@@ -544,16 +544,17 @@ EXPORT_SYMBOL(geni_se_clk_tbl_get); 
 * @se:		Pointer to the concerned serial engine.

 * @req_freq:	Requested clock frequency.

 * @index:	Index of the resultant frequency in the table.

 * @res_freq:	Resultant frequency which matches or is closer to the

 *		requested frequency.

 * @res_freq:	Resultant frequency of the source clock.

 * @exact:	Flag to indicate exact multiple requirement of the requested

 *		frequency.

 *

 * This function is called by the protocol drivers to determine the matching

 * or exact multiple of the requested frequency, as provided by the serial

 * engine clock in order to meet the performance requirements. If there is

 * no matching or exact multiple of the requested frequency found, then it

 * selects the closest floor frequency, if exact flag is not set.

 * This function is called by the protocol drivers to determine the best match

 * of the requested frequency as provided by the serial engine clock in order

 * to meet the performance requirements.

 *

 * If we return success:

 * - if @exact is true  then @res_freq / <an_integer> == @req_freq

 * - if @exact is false then @res_freq / <an_integer> <= @req_freq

 *

 * Return: 0 on success, standard Linux error codes on failure.

 */
@@ -564,6 +565,9 @@ int geni_se_clk_freq_match(struct geni_se *se, unsigned long req_freq, 
	unsigned long *tbl;

	int num_clk_levels;

	int i;

	unsigned long best_delta;

	unsigned long new_delta;

	unsigned int divider;



	num_clk_levels = geni_se_clk_tbl_get(se, &tbl);

	if (num_clk_levels < 0)
@@ -572,18 +576,21 @@ int geni_se_clk_freq_match(struct geni_se *se, unsigned long req_freq, 
	if (num_clk_levels == 0)

		return -EINVAL;



	*res_freq = 0;

	best_delta = ULONG_MAX;

	for (i = 0; i < num_clk_levels; i++) {

		if (!(tbl[i] % req_freq)) {

		divider = DIV_ROUND_UP(tbl[i], req_freq);

		new_delta = req_freq - tbl[i] / divider;

		if (new_delta < best_delta) {

			/* We have a new best! */

			*index = i;

			*res_freq = tbl[i];



			/* If the new best is exact then we're done */

			if (new_delta == 0)

				return 0;

		}



		if (!(*res_freq) || ((tbl[i] > *res_freq) &&

				     (tbl[i] < req_freq))) {

			*index = i;

			*res_freq = tbl[i];

			/* Record how close we got */

			best_delta = new_delta;

		}

	}