Re: [RESEND PATCH v6 2/3] leds: Add driver for the TLC5925 LED controller

[Jean-Jacques Hiblot]

On 04/08/2022 23:04, Pavel Machek wrote:
> On Thu 2022-08-04 22:23:00, Jean-Jacques Hiblot wrote:
> > On 31/07/2022 21:28, Andy Shevchenko wrote:
> > > On Fri, Jul 22, 2022 at 10:14 AM Jean-Jacques Hiblot
> > > <jjhiblot@xxxxxxxxxxxxxxx> wrote:
> > > > The TLC5925 is a 16-channels constant-current LED sink driver.
> > > > It is controlled via SPI but doesn't offer a register-based interface.
> > > > Instead it contains a shift register and latches that convert the
> > > > serial input into a parallel output.
> > > >
> > > > Datasheet: https://www.ti.com/lit/ds/symlink/tlc5925.pdf
> > > > Signed-off-by: Jean-Jacques Hiblot <jjhiblot@xxxxxxxxxxxxxxx>
> > > > Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> > > Sorry for my slowpokeness, but I just realized that this driver may
> > > not be needed. What is the difference to existing gpio-74x164?
> > It might work. However it might not be as practical and efficient as the
> > dedicated LED driver.
> >
> > I'll give a try.
> It is certainly preffered solution. If you decide to re-submit the
> driver anyway, please mention that we already have GPIO driver for
> compatible chip, and explain why this is superior.

Hi all,

sorry for the delay. I tried with the  74x164 gpio driver and it works 
as expected.

The only drawbacks are:

- as-is the 74x164 gpio driver supports only one output-enable gpio. 
However in practice I don't think multiple OE GPIOs will ever be used.

- with this approach, every time a LED status is changed the whole 
register has to be sent on the SPI bus. In other words, changes cannot 
be coalesced.


I don't know if this is enough to make a dedicated TLC5925 driver 
desirable in the kernel.

JJ

> Thanks,
> 								Pavel