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soc: qcom: geni: geni_se_clk_freq_match() should always accept multiples 

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: eddac5af06 ("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>
This commit is contained in:
Douglas Anderson 2018-09-06 15:49:06 -07:00 committed by Andy Gross
parent e11bbcedec
commit 867d4aa701
1 changed files with 22 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
drivers/soc/qcom/qcom-geni-se.c
View File

@ -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;
}
}