Hi Rishi,
the use case is to use/control the GPIOs of the MCP2221 without the need to
previously configure the GP pins manually by reprogramming the internal flash
(what tool would you use for this BTW?). Here we initially had a hard time to
make the GPIOs of the MCP2221 work (besides the missing HIDRAW support causing
a NULL pointer dereference, see my previous patch). All we got was "no such
file or directory" when trying to use/control the GPIOs, no matter whether via
gpioset or through sysfs. Only after diving into the source code and the
datasheet we realized -ENOENT was coming from a missing configuration of the GP
pins so that's why I started implementing the missing pieces.
Long story short: as a user I expect that a pin acts as a GPIO as soon as the
corresponding GPIO line is actively requested (via libgpiod or sysfs export).
There's no reason to keep the settings for a GP pin at an alternate function
if the user wishes to use it as a GPIO. If the user does not request the GPIO
line, all settings remain unchanged when using the driver (e.g. for I2C
access).
Best regards
Tobias
On 2021/08/19 17:29:14 CEST rishi gupta wrote:
> Thanks Tobias for the patch.
> I am just wondering what is the use case for this.
>
> On Wed, Aug 18, 2021, 8:58 PM Tobias Junghans <tobias.junghans@xxxxxxxx>
>
> wrote:
> > Per default the GP pins of an MCP2221 are designated to a certain
> > dedicated or alternate function. While it's possible to change these
> > defaults by manually updating the internal flash, it's much more
> > convenient and safe to configure the GP pins as GPIOs automatically
> > at runtime whenever the corresponding GPIO line is requested. The
> > previous setting is restored as soon as the GPIO line is freed again.
> >
> > Signed-off-by: Tobias Junghans <tobias.junghans@xxxxxxxx>
> > ---
> >
> > drivers/hid/hid-mcp2221.c | 142 ++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 142 insertions(+)
> >
> > diff --git a/drivers/hid/hid-mcp2221.c b/drivers/hid/hid-mcp2221.c
> > index 8e54173b195c..0f2345bd065f 100644
> > --- a/drivers/hid/hid-mcp2221.c
> > +++ b/drivers/hid/hid-mcp2221.c
> > @@ -30,6 +30,8 @@ enum {
> >
> > MCP2221_I2C_CANCEL = 0x10,
> > MCP2221_GPIO_SET = 0x50,
> > MCP2221_GPIO_GET = 0x51,
> >
> > + MCP2221_SRAM_SETTINGS_SET = 0x60,
> > + MCP2221_SRAM_SETTINGS_GET = 0x61,
> >
> > };
> >
> > /* Response codes in a raw input report */
> >
> > @@ -56,6 +58,7 @@ enum {
> >
> > };
> >
> > #define MCP_NGPIO 4
> >
> > +#define MCP_PASSWD_LEN 8
> >
> > /* MCP GPIO set command layout */
> > struct mcp_set_gpio {
> >
> > @@ -79,6 +82,49 @@ struct mcp_get_gpio {
> >
> > } gpio[MCP_NGPIO];
> >
> > } __packed;
> >
> > +/* MCP GP settings */
> > +enum {
> > + MCP2221_GP_FUNC_GPIO = 0x00, /* GPIO operation */
> > + MCP2221_GP_FUNC_DEDICATED = 0x01, /* dedicated function operation
> > */
> > + MCP2221_GP_FUNC_ALT0 = 0x02, /* alternate function 0 */
> > + MCP2221_GP_FUNC_ALT1 = 0x03, /* alternate function 1 */
> > + MCP2221_GP_FUNC_ALT2 = 0x04, /* alternate function 2 */
> > + MCP2221_GP_GPIO_DIR_IN = 0x08, /* GPIO input mode */
> > + MCP2221_GP_GPIO_OUT_VALUE = 0x10, /* GPIO output value */
> > +};
> > +
> > +/* MCP SRAM settings set command layout */
> > +struct mcp_set_sram_settings {
> > + u8 cmd;
> > + u8 dummy;
> > + u8 clk_out_div;
> > + u8 dac_voltage_ref;
> > + u8 dac_output_value;
> > + u8 adc_voltage_ref;
> > + u8 interrupt_detection;
> > + u8 alter_gp_settings;
> > + u8 gp_settings[MCP_NGPIO];
> > +} __packed;
> > +
> > +/* MCP SRAM settings set command layout */
> > +struct mcp_get_sram_settings {
> > + u8 cmd;
> > + u8 dummy;
> > + u8 len_chip_settings;
> > + u8 len_gp_settings;
> > + u8 init_values;
> > + u8 clk_out_div;
> > + u8 dac_settings;
> > + u8 interrupt_adc_settings;
> > + u16 usb_vid;
> > + u16 usb_pid;
> > + u8 usb_pwr_attrs;
> > + u8 usb_req_current;
> > + u8 password[MCP_PASSWD_LEN];
> > + u8 gp_settings[MCP_NGPIO];
> > +} __packed;
> > +
> > +
> >
> > /*
> >
> > * There is no way to distinguish responses. Therefore next command
> > * is sent only after response to previous has been received. Mutex
> >
> > @@ -97,6 +143,8 @@ struct mcp2221 {
> >
> > struct gpio_chip *gc;
> > u8 gp_idx;
> > u8 gpio_dir;
> >
> > + u8 gp_default_settings[MCP_NGPIO];
> > + u8 gp_runtime_settings[MCP_NGPIO];
> >
> > };
> >
> > /*
> >
> > @@ -668,6 +716,63 @@ static int mcp_gpio_get_direction(struct gpio_chip
> > *gc,
> >
> > return GPIO_LINE_DIRECTION_OUT;
> >
> > }
> >
> > +static int mcp_get_gp_default_settings(struct mcp2221 *mcp)
> > +{
> > + int ret;
> > +
> > + mcp->txbuf[0] = MCP2221_SRAM_SETTINGS_GET;
> > +
> > + mutex_lock(&mcp->lock);
> > + ret = mcp_send_data_req_status(mcp, mcp->txbuf, 1);
> > + mutex_unlock(&mcp->lock);
> > +
> > + return ret;
> > +}
> > +
> > +static int mcp_configure_gp(struct mcp2221 *mcp, unsigned int offset, u8
> > val)
> > +{
> > + int ret;
> > +
> > + memset(mcp->txbuf, 0, sizeof(struct mcp_set_sram_settings));
> > +
> > + mcp->txbuf[0] = MCP2221_SRAM_SETTINGS_SET;
> > + mcp->txbuf[offsetof(struct mcp_set_sram_settings,
> > alter_gp_settings)] = 0x80;
> > +
> > + mcp->gp_runtime_settings[offset] = val;
> > + mcp->gp_idx = offsetof(struct mcp_set_sram_settings,
> > gp_settings[0]);
> > + memcpy(&mcp->txbuf[mcp->gp_idx], mcp->gp_runtime_settings,
> > + sizeof(mcp->gp_runtime_settings));
> > +
> > + mutex_lock(&mcp->lock);
> > + ret = mcp_send_data_req_status(mcp, mcp->txbuf, sizeof(struct
> > mcp_set_sram_settings));
> > + mutex_unlock(&mcp->lock);
> > +
> > + return ret;
> > +}
> > +
> > +static int mcp_gpio_request(struct gpio_chip *gc, unsigned int offset)
> > +{
> > + int ret;
> > + struct mcp2221 *mcp = gpiochip_get_data(gc);
> > +
> > + ret = mcp_configure_gp(mcp, offset, MCP2221_GP_FUNC_GPIO |
> > + MCP2221_GP_GPIO_DIR_IN);
> > + if (ret) {
> > + hid_err(mcp->hdev, "failed to set GP function\n");
> > + return ret;
> > + }
> > +
> > + return ret;
> > +}
> > +
> > +static void mcp_gpio_free(struct gpio_chip *gc, unsigned int offset)
> > +{
> > + struct mcp2221 *mcp = gpiochip_get_data(gc);
> > +
> > + if (mcp_configure_gp(mcp, offset,
> > mcp->gp_default_settings[offset]))
> > + hid_warn(mcp->hdev, "failed to restore GP function\n");
> > +}
> > +
> >
> > /* Gives current state of i2c engine inside mcp2221 */
> > static int mcp_get_i2c_eng_state(struct mcp2221 *mcp,
> >
> > u8 *data, u8 idx)
> >
> > @@ -813,6 +918,28 @@ static int mcp2221_raw_event(struct hid_device *hdev,
> >
> > complete(&mcp->wait_in_report);
> > break;
> >
> > + case MCP2221_SRAM_SETTINGS_GET:
> > + if (data[1] == MCP2221_SUCCESS) {
> > + int offset = offsetof(struct
> > mcp_get_sram_settings, gp_settings[0]);
> > +
> > + memcpy(mcp->gp_default_settings, &data[offset],
> > +
> >
> > sizeof(mcp->gp_default_settings));
> >
> > + mcp->status = 0;
> > + } else {
> > + mcp->status = -EIO;
> > + }
> > + complete(&mcp->wait_in_report);
> > + break;
> > +
> > + case MCP2221_SRAM_SETTINGS_SET:
> > + if (data[1] == MCP2221_SUCCESS)
> > + mcp->status = 0;
> > + else
> > + mcp->status = -EIO;
> > +
> > + complete(&mcp->wait_in_report);
> > + break;
> > +
> >
> > default:
> > mcp->status = -EIO;
> > complete(&mcp->wait_in_report);
> >
> > @@ -890,6 +1017,8 @@ static int mcp2221_probe(struct hid_device *hdev,
> >
> > mcp->gc->get_direction = mcp_gpio_get_direction;
> > mcp->gc->set = mcp_gpio_set;
> > mcp->gc->get = mcp_gpio_get;
> >
> > + mcp->gc->request = mcp_gpio_request;
> > + mcp->gc->free = mcp_gpio_free;
> >
> > mcp->gc->ngpio = MCP_NGPIO;
> > mcp->gc->base = -1;
> > mcp->gc->can_sleep = 1;
> >
> > @@ -902,6 +1031,19 @@ static int mcp2221_probe(struct hid_device *hdev,
> >
> > if (ret)
> >
> > goto err_gc;
> >
> > + hid_device_io_start(hdev);
> > + ret = mcp_get_gp_default_settings(mcp);
> > + hid_device_io_stop(hdev);
> > +
> > + if (ret) {
> > + hid_err(mcp->hdev, "failed to get GP default settings\n");
> > + ret = -EIO;
> > + goto err_gc;
> > + }
> > +
> > + memcpy(mcp->gp_runtime_settings, mcp->gp_default_settings,
> > + sizeof(mcp->gp_default_settings));
> > +
> >
> > return 0;
> >
> > err_gc:
> > --
> > 2.25.1
