Re: [PATCH v2 6/7] USB: serial: ftdi_sio: Fix custom_divisor and c_*speed for ASYNC_SPD_CUST

["Pali Rohár" <pali@kernel.org>]

On Tuesday 13 September 2022 16:59:22 Johan Hovold wrote:
> On Thu, Aug 18, 2022 at 04:09:52PM +0200, Pali Rohár wrote:
> > On Sunday 24 July 2022 15:08:09 Johan Hovold wrote:
> > > On Sun, Jul 24, 2022 at 02:59:08PM +0200, Pali Rohár wrote:
> > > > On Sunday 24 July 2022 14:54:58 Johan Hovold wrote:
> > > > > On Sun, Jul 24, 2022 at 02:33:51PM +0200, Pali Rohár wrote:
> > > 
> > > > > > What is updated is the real baudrate in c_ispeed and c_ospeed
> > > > > > extensions.
> > > > > > 
> > > > > > It is really wrong? I thought that c_cflag should stay unchanged at
> > > > > > B38400 when ASYNC_SPD_CUST is used.
> > > > > 
> > > > > Yeah, cflags stay unchanged, but you shouldn't touch those fields when
> > > > > using the deprecated ASYNC_SPD_CUST hack.
> > > > 
> > > > Hm... Why? I thought that new extended fields (c_ispeed and c_ospeed)
> > > > should contain current real speed. What is the reason that c_*speed
> > > > fields should have 38400 when ASYNC_SPD_CUST hack is set?
> > > 
> > > Because we shouldn't go adding new features built around the deprecated
> > > ASYNC_SPD_CUST hack.
> > 
> > But this is not a new feature in the old deprecated hack. It for the
> > new interface.
> 
> I think I understand what you're getting at, but no. Let's not add more
> features built around ASYNC_SPD_CUST.
> 
> Johan

Seems that you did not understand the point. So I will try to explain it
again. This is not a new feature for _old_ ASYNC_SPD_CUST. This is the
fix for the _new_ TCGETS2 API, to ensure that driver will always returns
corrects values in c_*speed fields. If driver is not going to fix this
_new_ TCGETS2 API then there is _NO_ point to use this new API in
userspace and it is better to stick with the old ASYNC_SPD_CUST. And
this is the current userspace state. So based on your input, it is the
time to deprecate TCGETS2?