| From d9859839fa58eefda8c9e5e1913f9e593d76f4cf Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Thu, 6 Sep 2018 15:49:06 -0700 |
| Subject: soc: qcom: geni: geni_se_clk_freq_match() should always accept |
| multiples |
| |
| From: Douglas Anderson <dianders@chromium.org> |
| |
| [ 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: eddac5af0654 ("soc: qcom: Add GENI based QUP Wrapper driver") |
| Signed-off-by: Douglas Anderson <dianders@chromium.org> |
| Reviewed-by: Matthias Kaehlcke <mka@chromium.org> |
| Signed-off-by: Andy Gross <andy.gross@linaro.org> |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| drivers/soc/qcom/qcom-geni-se.c | 37 ++++++++++++++++++++------------- |
| 1 file changed, 22 insertions(+), 15 deletions(-) |
| |
| diff --git a/drivers/soc/qcom/qcom-geni-se.c b/drivers/soc/qcom/qcom-geni-se.c |
| index 1b19b8428c4ac..ee89ffb6dde84 100644 |
| --- a/drivers/soc/qcom/qcom-geni-se.c |
| +++ b/drivers/soc/qcom/qcom-geni-se.c |
| @@ -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]; |
| - return 0; |
| - } |
| |
| - if (!(*res_freq) || ((tbl[i] > *res_freq) && |
| - (tbl[i] < req_freq))) { |
| - *index = i; |
| - *res_freq = tbl[i]; |
| + /* If the new best is exact then we're done */ |
| + if (new_delta == 0) |
| + return 0; |
| + |
| + /* Record how close we got */ |
| + best_delta = new_delta; |
| } |
| } |
| |
| -- |
| 2.20.1 |
| |