Hi Dave
On Thu, Oct 06, 2022 at 03:44:54PM +0100, Dave Stevenson wrote:
> Hi Jacopo
>
> On Wed, 5 Oct 2022 at 20:07, Jacopo Mondi <jacopo@xxxxxxxxxx> wrote:
> >
> > Add support for V4L2_CID_ANALOG_GAIN. The control programs the global
> > gain register which applies to all color channels.
> >
> > As both the global digital and analog gains are controlled through a
> > single register, in order not to overwrite the configured digital gain
> > we need to read the current register value before modifying it.
> >
> > Implement a function to read register values and use it before applying
> > the new analog gain.
> >
> > Signed-off-by: Jacopo Mondi <jacopo@xxxxxxxxxx>
> > ---
> > drivers/media/i2c/ar0521.c | 64 ++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 64 insertions(+)
> >
> > diff --git a/drivers/media/i2c/ar0521.c b/drivers/media/i2c/ar0521.c
> > index 89f3c01f18ce..581f5e42994d 100644
> > --- a/drivers/media/i2c/ar0521.c
> > +++ b/drivers/media/i2c/ar0521.c
> > @@ -5,6 +5,8 @@
> > * Written by Krzysztof Hałasa
> > */
> >
> > +#include <asm/unaligned.h>
> > +
> > #include <linux/clk.h>
> > #include <linux/delay.h>
> > #include <linux/pm_runtime.h>
> > @@ -35,6 +37,11 @@
> > #define AR0521_HEIGHT_BLANKING_MIN 38u /* must be even */
> > #define AR0521_TOTAL_WIDTH_MIN 2968u
> >
> > +#define AR0521_ANA_GAIN_MIN 0x00
> > +#define AR0521_ANA_GAIN_MAX 0x3f
> > +#define AR0521_ANA_GAIN_STEP 0x01
> > +#define AR0521_ANA_GAIN_DEFAULT 0x00
> > +
> > /* AR0521 registers */
> > #define AR0521_REG_VT_PIX_CLK_DIV 0x0300
> > #define AR0521_REG_FRAME_LENGTH_LINES 0x0340
> > @@ -55,6 +62,7 @@
> > #define AR0521_REG_RED_GAIN 0x305A
> > #define AR0521_REG_GREEN2_GAIN 0x305C
> > #define AR0521_REG_GLOBAL_GAIN 0x305E
> > +#define AR0521_REG_GLOBAL_GAIN_ANA_MASK 0x3f
> >
> > #define AR0521_REG_HISPI_TEST_MODE 0x3066
> > #define AR0521_REG_HISPI_TEST_MODE_LP11 0x0004
> > @@ -77,6 +85,7 @@ static const char * const ar0521_supply_names[] = {
> >
> > struct ar0521_ctrls {
> > struct v4l2_ctrl_handler handler;
> > + struct v4l2_ctrl *ana_gain;
> > struct {
> > struct v4l2_ctrl *gain;
> > struct v4l2_ctrl *red_balance;
> > @@ -167,6 +176,36 @@ static int ar0521_write_reg(struct ar0521_dev *sensor, u16 reg, u16 val)
> > return ar0521_write_regs(sensor, buf, 2);
> > }
> >
> > +static int ar0521_read_reg(struct ar0521_dev *sensor, u16 reg, u16 *val)
> > +{
> > + struct i2c_client *client = sensor->i2c_client;
> > + unsigned char buf[2];
> > + struct i2c_msg msg;
> > + int ret;
> > +
> > + msg.addr = client->addr;
> > + msg.flags = client->flags;
> > + msg.len = sizeof(u16);
> > + msg.buf = buf;
> > + put_unaligned_be16(reg, buf);
> > +
> > + ret = i2c_transfer(client->adapter, &msg, 1);
> > + if (ret < 0)
> > + return ret;
> > +
> > + msg.len = sizeof(u16);
> > + msg.flags = client->flags | I2C_M_RD;
> > + msg.buf = buf;
> > +
> > + ret = i2c_transfer(client->adapter, &msg, 1);
> > + if (ret < 0)
> > + return ret;
> > +
> > + *val = get_unaligned_be16(buf);
> > +
> > + return 0;
> > +}
> > +
> > static int ar0521_set_geometry(struct ar0521_dev *sensor)
> > {
> > /* All dimensions are unsigned 12-bit integers */
> > @@ -187,6 +226,21 @@ static int ar0521_set_geometry(struct ar0521_dev *sensor)
> > return ar0521_write_regs(sensor, regs, ARRAY_SIZE(regs));
> > }
> >
> > +static int ar0521_set_analog_gain(struct ar0521_dev *sensor)
> > +{
> > + u16 global_gain;
> > + int ret;
> > +
> > + ret = ar0521_read_reg(sensor, AR0521_REG_GLOBAL_GAIN, &global_gain);
> > + if (ret)
> > + return ret;
> > +
> > + global_gain &= ~AR0521_REG_GLOBAL_GAIN_ANA_MASK;
> > + global_gain |= sensor->ctrls.ana_gain->val & AR0521_REG_GLOBAL_GAIN_ANA_MASK;
> > +
> > + return ar0521_write_reg(sensor, AR0521_REG_GLOBAL_GAIN, global_gain);
>
> Does this work without nasty interactions?
>
It seems so :)
> The register reference I have says that the bits 6:0 of 0x3056,
> 0x3058, 0x305a, 0x305c, and 0x305e are all aliased to register 0x3056.
> That means that the writes from ar0521_set_gains for GAIN,
> RED_BALANCE, and BLUE_BALANCE will stomp over your ANALOGUE_GAIN.
>
but you're right the interactions between the registers are not 100%
clear to me yet.
The fact is that libcamera only manipulates ANALOGUE_GAIN while the
other gains are not changed. I guess if one wants to manipulate the
single gains individually this is possible, but when setting the
global gain they will be overwritten ? This seems to be confirmed from
my experiments where changing the BLUE/RED gains has no visible
effects on the image as libcamera constantly adjusts the global gain
> I also don't see a call to __v4l2_ctrl_handler_setup from
> ar0521_set_stream, so whilst there is an explicit call to
> ar0521_set_gains, ANALOGUE_GAIN won't be set.
>
See [PATCH 08/10] media: ar0521: Setup controls at s_stream time
later in the series :)
> Dave
>
> [1] https://github.com/torvalds/linux/blob/master/drivers/media/i2c/ar0521.c#L190
>
> > +}
> > +
> > static int ar0521_set_gains(struct ar0521_dev *sensor)
> > {
> > int green = sensor->ctrls.gain->val;
> > @@ -456,6 +510,9 @@ static int ar0521_s_ctrl(struct v4l2_ctrl *ctrl)
> > case V4L2_CID_VBLANK:
> > ret = ar0521_set_geometry(sensor);
> > break;
> > + case V4L2_CID_ANALOGUE_GAIN:
> > + ret = ar0521_set_analog_gain(sensor);
> > + break;
> > case V4L2_CID_GAIN:
> > case V4L2_CID_RED_BALANCE:
> > case V4L2_CID_BLUE_BALANCE:
> > @@ -499,6 +556,13 @@ static int ar0521_init_controls(struct ar0521_dev *sensor)
> > /* We can use our own mutex for the ctrl lock */
> > hdl->lock = &sensor->lock;
> >
> > + /* Analog gain */
> > + ctrls->ana_gain = v4l2_ctrl_new_std(hdl, ops, V4L2_CID_ANALOGUE_GAIN,
> > + AR0521_ANA_GAIN_MIN,
> > + AR0521_ANA_GAIN_MAX,
> > + AR0521_ANA_GAIN_STEP,
> > + AR0521_ANA_GAIN_DEFAULT);
> > +
> > /* Manual gain */
> > ctrls->gain = v4l2_ctrl_new_std(hdl, ops, V4L2_CID_GAIN, 0, 511, 1, 0);
> > ctrls->red_balance = v4l2_ctrl_new_std(hdl, ops, V4L2_CID_RED_BALANCE,
> > --
> > 2.37.3
> >
