On Thursday 13 April 2017 08:57 PM, Thierry Reding wrote:
* PGP Signed by an unknown key
On Thu, Apr 13, 2017 at 07:40:28PM +0530, Laxman Dewangan wrote:
The PWM hardware IP is taped-out with different maximum frequency
on different SoCs.
From HW team:
For Tegra210, it is 38.4MHz.
For Tegra186, it is 102MHz.
Add support to limit the clock source frequency to the maximum IP
supported frequency. Provide these values via SoC chipdata.
Signed-off-by: Laxman Dewangan <ldewangan@xxxxxxxxxx>
---
drivers/pwm/pwm-tegra.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/drivers/pwm/pwm-tegra.c b/drivers/pwm/pwm-tegra.c
index 8c6ed55..7016c08 100644
--- a/drivers/pwm/pwm-tegra.c
+++ b/drivers/pwm/pwm-tegra.c
@@ -41,6 +41,9 @@
struct tegra_pwm_soc {
unsigned int num_channels;
+
+ /* Maximum IP frequency for given SoCs */
+ unsigned long max_frequency;
};
struct tegra_pwm_chip {
@@ -204,6 +207,24 @@ static int tegra_pwm_probe(struct platform_device *pdev)
/* Read PWM clock rate from source */
pwm->clk_rate = clk_get_rate(pwm->clk);
+ /* Make sure clock source freqeuncy must less than IP supported */
+ if (pwm->soc->max_frequency &&
+ (pwm->soc->max_frequency < pwm->clk_rate)) {
+ ret = clk_set_rate(pwm->clk, pwm->soc->max_frequency);
+ if (ret < 0) {
+ dev_err(&pdev->dev, "Failed to set max frequency: %d\n",
+ ret);
+ return ret;
+ }
+
+ /*
+ * The requested and configured frequency may differ due to
+ * clock register resolutions. Get the configured frequency
+ * so that PWM period can be calculated more accurately.
+ */
+ pwm->clk_rate = clk_get_rate(pwm->clk);
+ }
Is there a reason to conditionalize this? Couldn't we simply set the
clock to the maximum frequency in all cases? Higher frequency means
higher precision, right?
I think higher precision is not related directly to maximum frequency.
Precision will much depends on the perfect multiples between period and
clock source frequency.
If some usecases needed the perfect periods then the clock source
frequency can be set via clock init table for clock driver to achieve
the perfect PWM period. on this case, we should not change it in the PWM
driver.
PWM driver should only worry about to limit the maximum.
So just something like this perhaps:
ret = clk_set_rate(pwm->clk, pwm->soc->max_frequency);
if (ret < 0) {
...
}
pwm->clk_rate = clk_get_rate(pwm->clk);
That of course means that we'd need to define a maximum frequency for
SoCs prior to Tegra210. Any chance we can get at them?
Getting information for the older SoCs are little bit difficult. Let me
try if possible from HW team.
Otherwise, What we can do now as we can make 38.4MHz till T210 and 102M
for T186.
+
pwm->rst = devm_reset_control_get(&pdev->dev, "pwm");
if (IS_ERR(pwm->rst)) {
ret = PTR_ERR(pwm->rst);
@@ -275,12 +296,19 @@ static const struct tegra_pwm_soc tegra20_pwm_soc = {
.num_channels = 4,
};
+static const struct tegra_pwm_soc tegra210_pwm_soc = {
+ .num_channels = 4,
+ .max_frequency = 38400000UL, /* 38.4MHz */
+};
+
static const struct tegra_pwm_soc tegra186_pwm_soc = {
.num_channels = 1,
+ .max_frequency = 102000000UL, /* 102MHz */
I don't think we need these comments, it's fairly obvious what
frequencies you're specifying there. =)
Thierry
* Unknown Key
* 0x7F3EB3A1
--
To unsubscribe from this list: send the line "unsubscribe linux-tegra" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
