Re: [PATCH v2 6/8] drm/i915: Add function to output Aksv over GMBUS

From: Sean Paul
Date: Fri Dec 01 2017 - 14:17:47 EST

On Fri, Dec 1, 2017 at 2:06 PM, Ville SyrjÃlÃ
<ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> On Fri, Dec 01, 2017 at 12:20:28PM -0500, Sean Paul wrote:
>> Once the Aksv is available in the PCH, we need to get it on the wire to
>> the receiver via DDC. The hardware doesn't allow us to read the value
>> directly, so we need to tell GMBUS to source the Aksv internally and
>> send it to the right offset on the receiver.
>>
>> The way we do this is to initiate an indexed write where the index is
>> the Aksv register offset. We write dummy values to GMBUS3 as if we were
>> sending the key, and the hardware slips in the "real" values when it
>> goes out.
>>
>> Changes in v2:
>> - None
>>
>> Signed-off-by: Sean Paul <seanpaul@xxxxxxxxxxxx>
>> ---
>> drivers/gpu/drm/i915/i915_drv.h | 1 +
>> drivers/gpu/drm/i915/i915_reg.h | 1 +
>> drivers/gpu/drm/i915/intel_i2c.c | 54 ++++++++++++++++++++++++++++++++++------
>> 3 files changed, 48 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
>> index 36bb4927484a..10f740c9e571 100644
>> --- a/drivers/gpu/drm/i915/i915_drv.h
>> +++ b/drivers/gpu/drm/i915/i915_drv.h
>> @@ -4043,6 +4043,7 @@ extern int intel_setup_gmbus(struct drm_i915_private *dev_priv);
>> extern void intel_teardown_gmbus(struct drm_i915_private *dev_priv);
>> extern bool intel_gmbus_is_valid_pin(struct drm_i915_private *dev_priv,
>> unsigned int pin);
>> +extern int intel_gmbus_output_aksv(struct i2c_adapter *adapter);
>>
>> extern struct i2c_adapter *
>> intel_gmbus_get_adapter(struct drm_i915_private *dev_priv, unsigned int pin);
>> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
>> index 6dca305ccbf7..8b71a20882ca 100644
>> --- a/drivers/gpu/drm/i915/i915_reg.h
>> +++ b/drivers/gpu/drm/i915/i915_reg.h
>> @@ -3040,6 +3040,7 @@ enum i915_power_well_id {
>> # define GPIO_DATA_PULLUP_DISABLE (1 << 13)
>>
>> #define GMBUS0 _MMIO(dev_priv->gpio_mmio_base + 0x5100) /* clock/port select */
>> +#define GMBUS_AKSV_SELECT (1<<11)
>> #define GMBUS_RATE_100KHZ (0<<8)
>> #define GMBUS_RATE_50KHZ (1<<8)
>> #define GMBUS_RATE_400KHZ (2<<8) /* reserved on Pineview */
>> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
>> index eb5827110d8f..c01156bf0f27 100644
>> --- a/drivers/gpu/drm/i915/intel_i2c.c
>> +++ b/drivers/gpu/drm/i915/intel_i2c.c
>> @@ -30,6 +30,7 @@
>> #include <linux/i2c-algo-bit.h>
>> #include <linux/export.h>
>> #include <drm/drmP.h>
>> +#include <drm/drm_hdcp.h>
>> #include "intel_drv.h"
>> #include <drm/i915_drm.h>
>> #include "i915_drv.h"
>> @@ -373,7 +374,8 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
>>
>> static int
>> gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
>> - unsigned short addr, u8 *buf, unsigned int len)
>> + unsigned short addr, u8 *buf, unsigned int len,
>> + u32 gmbus1_index)
>> {
>> unsigned int chunk_size = len;
>> u32 val, loop;
>> @@ -386,7 +388,7 @@ gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
>>
>> I915_WRITE_FW(GMBUS3, val);
>> I915_WRITE_FW(GMBUS1,
>> - GMBUS_CYCLE_WAIT |
>> + gmbus1_index | GMBUS_CYCLE_WAIT |
>> (chunk_size << GMBUS_BYTE_COUNT_SHIFT) |
>> (addr << GMBUS_SLAVE_ADDR_SHIFT) |
>> GMBUS_SLAVE_WRITE | GMBUS_SW_RDY);
>> @@ -409,7 +411,8 @@ gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
>> }
>>
>> static int
>> -gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
>> +gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
>> + u32 gmbus1_index)
>> {
>> u8 *buf = msg->buf;
>> unsigned int tx_size = msg->len;
>> @@ -419,7 +422,8 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
>> do {
>> len = min(tx_size, GMBUS_BYTE_COUNT_MAX);
>>
>> - ret = gmbus_xfer_write_chunk(dev_priv, msg->addr, buf, len);
>> + ret = gmbus_xfer_write_chunk(dev_priv, msg->addr, buf, len,
>> + gmbus1_index);
>> if (ret)
>> return ret;
>>
>> @@ -470,7 +474,8 @@ gmbus_xfer_index_read(struct drm_i915_private *dev_priv, struct i2c_msg *msgs)
>> }
>>
>> static int
>> -do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
>> +do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num,
>> + u32 gmbus0_source, u32 gmbus1_index)
>> {
>> struct intel_gmbus *bus = container_of(adapter,
>> struct intel_gmbus,
>> @@ -480,7 +485,7 @@ do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
>> int ret = 0;
>>
>> retry:
>> - I915_WRITE_FW(GMBUS0, bus->reg0);
>> + I915_WRITE_FW(GMBUS0, gmbus0_source | bus->reg0);
>>
>> for (; i < num; i += inc) {
>> inc = 1;
>> @@ -490,7 +495,8 @@ do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
>> } else if (msgs[i].flags & I2C_M_RD) {
>> ret = gmbus_xfer_read(dev_priv, &msgs[i], 0);
>> } else {
>> - ret = gmbus_xfer_write(dev_priv, &msgs[i]);
>> + ret = gmbus_xfer_write(dev_priv, &msgs[i],
>> + gmbus1_index);
>> }
>>
>> if (!ret)
>> @@ -598,7 +604,7 @@ gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
>> if (ret < 0)
>> bus->force_bit &= ~GMBUS_FORCE_BIT_RETRY;
>> } else {
>> - ret = do_gmbus_xfer(adapter, msgs, num);
>> + ret = do_gmbus_xfer(adapter, msgs, num, 0, 0);
>> if (ret == -EAGAIN)
>> bus->force_bit |= GMBUS_FORCE_BIT_RETRY;
>> }
>> @@ -608,6 +614,38 @@ gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
>> return ret;
>> }
>>
>> +int intel_gmbus_output_aksv(struct i2c_adapter *adapter)
>> +{
>> + struct intel_gmbus *bus = container_of(adapter, struct intel_gmbus,
>> + adapter);
>> + struct drm_i915_private *dev_priv = bus->dev_priv;
>> + int ret;
>> + u8 buf[DRM_HDCP_KSV_LEN] = { 0 };
>> + struct i2c_msg msg = {
>> + .addr = DRM_HDCP_DDC_ADDR,
>> + .flags = 0,
>> + .len = sizeof(buf),
>> + .buf = buf,
>> + };
>> +
>> + intel_display_power_get(dev_priv, POWER_DOMAIN_GMBUS);
>> + mutex_lock(&dev_priv->gmbus_mutex);
>> +
>> + /*
>> + * In order to output Aksv to the receiver, use an indexed write to
>> + * pass the i2c command, and tell GMBUS to use the HW-provided value
>> + * instead of sourcing GMBUS3 for the data.
>> + */
>> + ret = do_gmbus_xfer(adapter, &msg, 1, GMBUS_AKSV_SELECT,
>> + GMBUS_CYCLE_INDEX |
>> + (DRM_HDCP_DDC_AKSV << GMBUS_SLAVE_INDEX_SHIFT));
>
> It might be nicer to just use two msgs here and modify
> gmbus_xfer_index_read() to support indexed writes as well.

I think two msgs implies a STOP bit in between. At least, that's how I
interpret "normal" writes.

> Would avoid having to pass in the GMBUS1 value all the way.

We could infer an indexed write if num_msgs == 1 && flags == 0 && len
> 1. However that would require us to assume that all single msg
writes have a command byte at the beginning of the transaction, which
might not be true for all i2c slaves.

Sean


>
> Not sure what to do with GMBUS_AKSV_SELECT. I guess either pass
> it in explicitly like you're doing here, or maybe add a small
> helper ala gmbus_is_index_read() so that do_gmbus_xfer() could
> sniff out which source we should use based on the passed in msgs?
>
>> +
>> + mutex_unlock(&dev_priv->gmbus_mutex);
>> + intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS);
>> +
>> + return ret;
>> +}
>> +
>> static u32 gmbus_func(struct i2c_adapter *adapter)
>> {
>> return i2c_bit_algo.functionality(adapter) &
>> --
>> 2.15.0.531.g2ccb3012c9-goog
>>
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>
> --
> Ville SyrjÃlÃ
> Intel OTC