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watchdog: renesas_wdt: apply better precision 

The error margin of the clks_per_second variable was too large and
caused offsets when used with clock frequencies which left a remainder
after applying the dividers. Now we always calculate directly using the
clock rate and the divider using some helper macros. That also means
that DIV_ROUND_UP moves from probe to the multiplication macro. In
probe, we don't need to ensure anymore that 'clks_per_sec' would go too
fast but rather ensure that the lower limit is really at least 1 to
certainly get a full cycle.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
This commit is contained in:
Wolfram Sang 2017-07-19 10:27:54 +02:00 committed by Wim Van Sebroeck
parent 1c1b243401
commit 82f64cd208
1 changed files with 19 additions and 9 deletions
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28
drivers/watchdog/renesas_wdt.c
View File

@ -26,6 +26,17 @@
#define RWDT_DEFAULT_TIMEOUT 60U
/*
* In probe, clk_rate is checked to be not more than 16 bit * biggest clock
* divider (10 bits). d is only a factor to fully utilize the WDT counter and
* will not exceed its 16 bits. Thus, no overflow, we stay below 32 bits.
*/
#define MUL_BY_CLKS_PER_SEC(p, d) \
DIV_ROUND_UP((d) * (p)->clk_rate, clk_divs[(p)->cks])
/* d is 16 bit, clk_divs 10 bit -> no 32 bit overflow */
#define DIV_BY_CLKS_PER_SEC(p, d) ((d) * clk_divs[(p)->cks] / (p)->clk_rate)
static const unsigned int clk_divs[] = { 1, 4, 16, 32, 64, 128, 1024 };
static bool nowayout = WATCHDOG_NOWAYOUT;
@ -37,7 +48,7 @@ struct rwdt_priv {
void __iomem *base;
struct watchdog_device wdev;
struct clk *clk;
unsigned long clks_per_sec;
unsigned long clk_rate;
u8 cks;
};
@ -55,7 +66,7 @@ static int rwdt_init_timeout(struct watchdog_device *wdev)
{
struct rwdt_priv *priv = watchdog_get_drvdata(wdev);
rwdt_write(priv, 65536 - wdev->timeout * priv->clks_per_sec, RWTCNT);
rwdt_write(priv, 65536 - MUL_BY_CLKS_PER_SEC(priv, wdev->timeout), RWTCNT);
return 0;
}
@ -92,7 +103,7 @@ static unsigned int rwdt_get_timeleft(struct watchdog_device *wdev)
struct rwdt_priv *priv = watchdog_get_drvdata(wdev);
u16 val = readw_relaxed(priv->base + RWTCNT);
return (65536 - val) / priv->clks_per_sec;
return DIV_BY_CLKS_PER_SEC(priv, 65536 - val);
}
static const struct watchdog_info rwdt_ident = {
@ -112,7 +123,7 @@ static int rwdt_probe(struct platform_device *pdev)
{
struct rwdt_priv *priv;
struct resource *res;
unsigned long rate, clks_per_sec;
unsigned long clks_per_sec;
int ret, i;
priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
@ -128,14 +139,13 @@ static int rwdt_probe(struct platform_device *pdev)
if (IS_ERR(priv->clk))
return PTR_ERR(priv->clk);
rate = clk_get_rate(priv->clk);
if (!rate)
priv->clk_rate = clk_get_rate(priv->clk);
if (!priv->clk_rate)
return -ENOENT;
for (i = ARRAY_SIZE(clk_divs) - 1; i >= 0; i--) {
clks_per_sec = DIV_ROUND_UP(rate, clk_divs[i]);
clks_per_sec = priv->clk_rate / clk_divs[i];
if (clks_per_sec && clks_per_sec < 65536) {
priv->clks_per_sec = clks_per_sec;
priv->cks = i;
break;
}
@ -153,7 +163,7 @@ static int rwdt_probe(struct platform_device *pdev)
priv->wdev.ops = &rwdt_ops,
priv->wdev.parent = &pdev->dev;
priv->wdev.min_timeout = 1;
priv->wdev.max_timeout = 65536 / clks_per_sec;
priv->wdev.max_timeout = DIV_BY_CLKS_PER_SEC(priv, 65536);
priv->wdev.timeout = min(priv->wdev.max_timeout, RWDT_DEFAULT_TIMEOUT);
platform_set_drvdata(pdev, priv);