On Wed, Jun 01, 2022 at 11:08:28PM +0200, Klaus Jensen wrote:
> From: Klaus Jensen <k.jensen@samsung.com>
> 
> Allow slaves to master the bus by registering a bottom halve. If the bus
> is busy, the bottom halve is queued up. When a slave has succesfully
                      ^ half
> mastered the bus, the bottom halve is scheduled.
                               ^ half

"halve" is a verb that means to split something into two pieces.  Yes,
English is a strange language :).

Also, technically from an I2C point of view, masters master the bus and
slaves only respond.  The way it's phrased here and elsewhere sounds a
little strange from that point of view.

I'm ok with this patch.  It's straightforward.

> 
> Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
> ---
>  hw/i2c/core.c        | 34 +++++++++++++++++++++++++++++++++-
>  include/hw/i2c/i2c.h | 14 ++++++++++++++
>  2 files changed, 47 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/i2c/core.c b/hw/i2c/core.c
> index d0cb2d32fa44..145dce60782a 100644
> --- a/hw/i2c/core.c
> +++ b/hw/i2c/core.c
> @@ -13,6 +13,7 @@
>  #include "migration/vmstate.h"
>  #include "qapi/error.h"
>  #include "qemu/module.h"
> +#include "qemu/main-loop.h"
>  #include "trace.h"
>  
>  #define I2C_BROADCAST 0x00
> @@ -62,6 +63,7 @@ I2CBus *i2c_init_bus(DeviceState *parent, const char *name)
>  
>      bus = I2C_BUS(qbus_new(TYPE_I2C_BUS, parent, name));
>      QLIST_INIT(&bus->current_devs);
> +    QSIMPLEQ_INIT(&bus->pending_masters);
>      vmstate_register(NULL, VMSTATE_INSTANCE_ID_ANY, &vmstate_i2c_bus, bus);
>      return bus;
>  }
> @@ -74,7 +76,7 @@ void i2c_slave_set_address(I2CSlave *dev, uint8_t address)
>  /* Return nonzero if bus is busy.  */
>  int i2c_bus_busy(I2CBus *bus)
>  {
> -    return !QLIST_EMPTY(&bus->current_devs);
> +    return !QLIST_EMPTY(&bus->current_devs) || bus->bh;
>  }
>  
>  bool i2c_scan_bus(I2CBus *bus, uint8_t address, bool broadcast,
> @@ -180,6 +182,26 @@ int i2c_start_transfer(I2CBus *bus, uint8_t address, bool is_recv)
>                                                 : I2C_START_SEND);
>  }
>  
> +void i2c_bus_master(I2CBus *bus, QEMUBH *bh)
> +{
> +    if (i2c_bus_busy(bus)) {
> +        I2CPendingMaster *node = g_new(struct I2CPendingMaster, 1);
> +        node->bh = bh;
> +
> +        QSIMPLEQ_INSERT_TAIL(&bus->pending_masters, node, entry);
> +
> +        return;
> +    }
> +
> +    bus->bh = bh;
> +    qemu_bh_schedule(bus->bh);
> +}
> +
> +void i2c_bus_release(I2CBus *bus)
> +{
> +    bus->bh = NULL;
> +}
> +
>  int i2c_start_recv(I2CBus *bus, uint8_t address)
>  {
>      return i2c_do_start_transfer(bus, address, I2C_START_RECV);
> @@ -206,6 +228,16 @@ void i2c_end_transfer(I2CBus *bus)
>          g_free(node);
>      }
>      bus->broadcast = false;
> +
> +    if (!QSIMPLEQ_EMPTY(&bus->pending_masters)) {
> +        I2CPendingMaster *node = QSIMPLEQ_FIRST(&bus->pending_masters);
> +        bus->bh = node->bh;
> +
> +        QSIMPLEQ_REMOVE_HEAD(&bus->pending_masters, entry);
> +        g_free(node);
> +
> +        qemu_bh_schedule(bus->bh);
> +    }
>  }
>  
>  int i2c_send(I2CBus *bus, uint8_t data)
> diff --git a/include/hw/i2c/i2c.h b/include/hw/i2c/i2c.h
> index 5ca3b708c0be..be8bb8b78a60 100644
> --- a/include/hw/i2c/i2c.h
> +++ b/include/hw/i2c/i2c.h
> @@ -69,13 +69,25 @@ struct I2CNode {
>      QLIST_ENTRY(I2CNode) next;
>  };
>  
> +typedef struct I2CPendingMaster I2CPendingMaster;
> +
> +struct I2CPendingMaster {
> +    QEMUBH *bh;
> +    QSIMPLEQ_ENTRY(I2CPendingMaster) entry;
> +};
> +
>  typedef QLIST_HEAD(I2CNodeList, I2CNode) I2CNodeList;
> +typedef QSIMPLEQ_HEAD(I2CPendingMasters, I2CPendingMaster) I2CPendingMasters;
>  
>  struct I2CBus {
>      BusState qbus;
>      I2CNodeList current_devs;
> +    I2CPendingMasters pending_masters;
>      uint8_t saved_address;
>      bool broadcast;
> +
> +    /* Set from slave currently mastering the bus. */
> +    QEMUBH *bh;
>  };
>  
>  I2CBus *i2c_init_bus(DeviceState *parent, const char *name);
> @@ -117,6 +129,8 @@ int i2c_start_send(I2CBus *bus, uint8_t address);
>  
>  void i2c_end_transfer(I2CBus *bus);
>  void i2c_nack(I2CBus *bus);
> +void i2c_bus_master(I2CBus *bus, QEMUBH *bh);
> +void i2c_bus_release(I2CBus *bus);
>  int i2c_send(I2CBus *bus, uint8_t data);
>  uint8_t i2c_recv(I2CBus *bus);
>  bool i2c_scan_bus(I2CBus *bus, uint8_t address, bool broadcast,
> -- 
> 2.36.1
>