Re: [PATCH maybe-7.2 1/3] hw/i2c: only schedule pending master when bus is idle

[Klaus Jensen]

On Nov 17 07:56, Cédric Le Goater wrote:
> On 11/17/22 07:40, Klaus Jensen wrote:
> > On Nov 16 16:58, Cédric Le Goater wrote:
> > > On 11/16/22 09:43, Klaus Jensen wrote:
> > > > From: Klaus Jensen <k.jensen@samsung.com>
> > > > 
> > > > It is not given that the current master will release the bus after a
> > > > transfer ends. Only schedule a pending master if the bus is idle.
> > > > 
> > > > Fixes: 37fa5ca42623 ("hw/i2c: support multiple masters")
> > > > Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
> > > > ---
> > > >    hw/i2c/aspeed_i2c.c  |  2 ++
> > > >    hw/i2c/core.c        | 37 ++++++++++++++++++++++---------------
> > > >    include/hw/i2c/i2c.h |  2 ++
> > > >    3 files changed, 26 insertions(+), 15 deletions(-)
> > > > 
> > > > diff --git a/hw/i2c/aspeed_i2c.c b/hw/i2c/aspeed_i2c.c
> > > > index c166fd20fa11..1f071a3811f7 100644
> > > > --- a/hw/i2c/aspeed_i2c.c
> > > > +++ b/hw/i2c/aspeed_i2c.c
> > > > @@ -550,6 +550,8 @@ static void aspeed_i2c_bus_handle_cmd(AspeedI2CBus 
> > > > *bus, uint64_t value)
> > > >            }
> > > >            SHARED_ARRAY_FIELD_DP32(bus->regs, reg_cmd, M_STOP_CMD, 0);
> > > >            aspeed_i2c_set_state(bus, I2CD_IDLE);
> > > > +
> > > > +        i2c_schedule_pending_master(bus->bus);
> > > 
> > > Shouldn't it be i2c_bus_release() ?
> > > 
> > 
> > The reason for having both i2c_bus_release() and
> > i2c_schedule_pending_master() is that i2c_bus_release() sort of pairs
> > with i2c_bus_master(). They either set or clear the bus->bh member.
> > 
> > In the current design, the controller (in this case the Aspeed I2C) is
> > an "implicit" master (it does not have a bottom half driving it), so
> > there is no bus->bh to clear.
> > 
> > I should (and will) write some documentation on the asynchronous API.
> 
> I found the routine names confusing. Thanks for the clarification.
> 
> Maybe we could do this rename  :
> 
>   i2c_bus_release()             -> i2c_bus_release_and_clear()
>   i2c_schedule_pending_master() -> i2c_bus_release()
> 
> and keep i2c_schedule_pending_master() internal the I2C core subsystem.
> 

How about renaming i2c_bus_master to i2c_bus_acquire() such that it
pairs with i2c_bus_release().

And then add an i2c_bus_yield() to be used by the controller? I think we
should be able to assert in i2c_bus_yield() that bus->bh is NULL. But
I'll take a closer look at that.

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