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Date: Tue, 30 Jan 2018 15:15:12 +1030
From: Joel Stanley <joel@....id.au>
To: Jeremy Kerr <jk@...abs.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Christopher Bostic <cbostic@...ux.vnet.ibm.com>,
Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 3/3] fsi/master-gpio: Add external mode
Hi Jeremy,
On Thu, Jun 22, 2017 at 7:40 AM, Jeremy Kerr <jk@...abs.org> wrote:
> This change introduces an 'external mode' for GPIO-based FSI masters,
> allowing the clock and data lines to be driven by an external source.
> For example, external mode is selected by a user when an external debug
> device is attached to the FSI pins.
>
> To do this, we need to set specific states for the trans, mux and enable
> gpios, and prevent access to clk & data from the FSI core code (by
> returning EBUSY).
>
> External mode is controlled by a sysfs attribute, so add the relevent
> information to Documentation/ABI/
>
> Signed-off-by: Jeremy Kerr <jk@...abs.org>
> Reviewed-by: Joel Stanley <joel@....id.au>
This one never made it into Greg's tree (I assume because we didn't cc him).
Can you resend with Greg on cc please?
Cheers,
Joel
> ---
> .../ABI/testing/sysfs-driver-fsi-master-gpio | 10 +++
> drivers/fsi/fsi-master-gpio.c | 78 +++++++++++++++++++++-
> 2 files changed, 86 insertions(+), 2 deletions(-)
> create mode 100644 Documentation/ABI/testing/sysfs-driver-fsi-master-gpio
>
> diff --git a/Documentation/ABI/testing/sysfs-driver-fsi-master-gpio b/Documentation/ABI/testing/sysfs-driver-fsi-master-gpio
> new file mode 100644
> index 0000000..9667bb4
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-driver-fsi-master-gpio
> @@ -0,0 +1,10 @@
> +What: /sys/bus/platform/devices/[..]/fsi-master-gpio/external_mode
> +Date: June 2017
> +KernelVersion: 4.12
> +Contact: jk@...abs.org
> +Description:
> + Controls access arbitration for GPIO-based FSI master. A
> + value of 0 (the default) sets normal mode, where the
> + driver performs FSI bus transactions, 1 sets external mode,
> + where the FSI bus is driven externally (for example, by
> + a debug device).
> diff --git a/drivers/fsi/fsi-master-gpio.c b/drivers/fsi/fsi-master-gpio.c
> index a6d602e..b54c213 100644
> --- a/drivers/fsi/fsi-master-gpio.c
> +++ b/drivers/fsi/fsi-master-gpio.c
> @@ -59,6 +59,7 @@ struct fsi_master_gpio {
> struct gpio_desc *gpio_trans; /* Voltage translator */
> struct gpio_desc *gpio_enable; /* FSI enable */
> struct gpio_desc *gpio_mux; /* Mux control */
> + bool external_mode;
> };
>
> #define CREATE_TRACE_POINTS
> @@ -411,6 +412,12 @@ static int fsi_master_gpio_xfer(struct fsi_master_gpio *master, uint8_t slave,
> int rc;
>
> spin_lock_irqsave(&master->cmd_lock, flags);
> +
> + if (master->external_mode) {
> + spin_unlock_irqrestore(&master->cmd_lock, flags);
> + return -EBUSY;
> + }
> +
> serial_out(master, cmd);
> echo_delay(master);
> rc = poll_for_response(master, slave, resp_len, resp);
> @@ -469,6 +476,10 @@ static int fsi_master_gpio_break(struct fsi_master *_master, int link)
> trace_fsi_master_gpio_break(master);
>
> spin_lock_irqsave(&master->cmd_lock, flags);
> + if (master->external_mode) {
> + spin_unlock_irqrestore(&master->cmd_lock, flags);
> + return -EBUSY;
> + }
> set_sda_output(master, 1);
> sda_out(master, 1);
> clock_toggle(master, FSI_PRE_BREAK_CLOCKS);
> @@ -497,25 +508,84 @@ static void fsi_master_gpio_init(struct fsi_master_gpio *master)
> clock_zeros(master, FSI_INIT_CLOCKS);
> }
>
> +static void fsi_master_gpio_init_external(struct fsi_master_gpio *master)
> +{
> + gpiod_direction_output(master->gpio_mux, 0);
> + gpiod_direction_output(master->gpio_trans, 0);
> + gpiod_direction_output(master->gpio_enable, 1);
> + gpiod_direction_input(master->gpio_clk);
> + gpiod_direction_input(master->gpio_data);
> +}
> +
> static int fsi_master_gpio_link_enable(struct fsi_master *_master, int link)
> {
> struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
> unsigned long flags;
> + int rc = -EBUSY;
>
> if (link != 0)
> return -ENODEV;
>
> spin_lock_irqsave(&master->cmd_lock, flags);
> - gpiod_set_value(master->gpio_enable, 1);
> + if (!master->external_mode) {
> + gpiod_set_value(master->gpio_enable, 1);
> + rc = 0;
> + }
> spin_unlock_irqrestore(&master->cmd_lock, flags);
>
> - return 0;
> + return rc;
> +}
> +
> +static ssize_t external_mode_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + struct fsi_master_gpio *master = dev_get_drvdata(dev);
> +
> + return snprintf(buf, PAGE_SIZE - 1, "%u\n",
> + master->external_mode ? 1 : 0);
> +}
> +
> +static ssize_t external_mode_store(struct device *dev,
> + struct device_attribute *attr, const char *buf, size_t count)
> +{
> + struct fsi_master_gpio *master = dev_get_drvdata(dev);
> + unsigned long flags, val;
> + bool external_mode;
> + int err;
> +
> + err = kstrtoul(buf, 0, &val);
> + if (err)
> + return err;
> +
> + external_mode = !!val;
> +
> + spin_lock_irqsave(&master->cmd_lock, flags);
> +
> + if (external_mode == master->external_mode) {
> + spin_unlock_irqrestore(&master->cmd_lock, flags);
> + return count;
> + }
> +
> + master->external_mode = external_mode;
> + if (master->external_mode)
> + fsi_master_gpio_init_external(master);
> + else
> + fsi_master_gpio_init(master);
> + spin_unlock_irqrestore(&master->cmd_lock, flags);
> +
> + fsi_master_rescan(&master->master);
> +
> + return count;
> }
>
> +static DEVICE_ATTR(external_mode, 0664,
> + external_mode_show, external_mode_store);
> +
> static int fsi_master_gpio_probe(struct platform_device *pdev)
> {
> struct fsi_master_gpio *master;
> struct gpio_desc *gpio;
> + int rc;
>
> master = devm_kzalloc(&pdev->dev, sizeof(*master), GFP_KERNEL);
> if (!master)
> @@ -572,6 +642,10 @@ static int fsi_master_gpio_probe(struct platform_device *pdev)
>
> fsi_master_gpio_init(master);
>
> + rc = device_create_file(&pdev->dev, &dev_attr_external_mode);
> + if (rc)
> + return rc;
> +
> return fsi_master_register(&master->master);
> }
>
> --
> 2.7.4
>
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