diff options
| author | Benjamin Herrenschmidt <benh@kernel.crashing.org> | 2018-05-08 11:06:38 +1000 |
|---|---|---|
| committer | Benjamin Herrenschmidt <benh@kernel.crashing.org> | 2018-06-12 14:04:41 +1000 |
| commit | bc1099d2b2519fa0f6c7613d8de398df8438a36b (patch) | |
| tree | 98cb568b10bff23b977ea82be4b8b804f34f5412 /drivers | |
| parent | 5d0d16f135c0cb7a12e417cbe12b271524ce4d40 (diff) | |
| download | linux-bc1099d2b2519fa0f6c7613d8de398df8438a36b.tar.bz2 | |
fsi/fsi-master-gpio: Add "no-gpio-delays" option
This adds support for an optional device-tree property that
makes the driver skip all the delays around clocking the
GPIOs and set it in the device-tree of common POWER9 based
OpenPower platforms.
This useful on chips like the AST2500 where the GPIO block is
running at a fairly low clock frequency (25Mhz typically). In
this case, the delays are unnecessary and due to the low
precision of the timers, actually quite harmful in terms of
performance.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Christopher Bostic <cbostic@linux.vnet.ibm.com>
Tested-by: Joel Stanley <joel@jms.id.au>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/fsi/fsi-master-gpio.c | 20 |
1 files changed, 16 insertions, 4 deletions
diff --git a/drivers/fsi/fsi-master-gpio.c b/drivers/fsi/fsi-master-gpio.c index d6508bbad1fb..c82bbd35276e 100644 --- a/drivers/fsi/fsi-master-gpio.c +++ b/drivers/fsi/fsi-master-gpio.c @@ -62,6 +62,7 @@ struct fsi_master_gpio { struct gpio_desc *gpio_enable; /* FSI enable */ struct gpio_desc *gpio_mux; /* Mux control */ bool external_mode; + bool no_delays; }; #define CREATE_TRACE_POINTS @@ -79,9 +80,11 @@ static void clock_toggle(struct fsi_master_gpio *master, int count) int i; for (i = 0; i < count; i++) { - ndelay(FSI_GPIO_STD_DLY); + if (!master->no_delays) + ndelay(FSI_GPIO_STD_DLY); gpiod_set_value(master->gpio_clk, 0); - ndelay(FSI_GPIO_STD_DLY); + if (!master->no_delays) + ndelay(FSI_GPIO_STD_DLY); gpiod_set_value(master->gpio_clk, 1); } } @@ -90,10 +93,12 @@ static int sda_clock_in(struct fsi_master_gpio *master) { int in; - ndelay(FSI_GPIO_STD_DLY); + if (!master->no_delays) + ndelay(FSI_GPIO_STD_DLY); gpiod_set_value(master->gpio_clk, 0); in = gpiod_get_value(master->gpio_data); - ndelay(FSI_GPIO_STD_DLY); + if (!master->no_delays) + ndelay(FSI_GPIO_STD_DLY); gpiod_set_value(master->gpio_clk, 1); return in ? 1 : 0; } @@ -677,6 +682,13 @@ static int fsi_master_gpio_probe(struct platform_device *pdev) } master->gpio_mux = gpio; + /* + * Check if GPIO block is slow enought that no extra delays + * are necessary. This improves performance on ast2500 by + * an order of magnitude. + */ + master->no_delays = device_property_present(&pdev->dev, "no-gpio-delays"); + master->master.n_links = 1; master->master.flags = FSI_MASTER_FLAG_SWCLOCK; master->master.read = fsi_master_gpio_read; |