Re: [EXT] Re: [PATCH v3 2/2] serial: 8250_dw: add Ambarella CV75 quirks

[Andy Shevchenko]

On Fri, Aug 14, 2026 at 12:10:34PM +0000, Long Zhao wrote:

> Originally we submitted a dedicated Ambarella UART driver. During review,
> Linus pointed out that the register layout is basically 8250-compatible
> and suggested reusing the existing 8250 code instead of maintaining a
> separate driver. That is how we ended up with the current approach of
> binding through 8250_dw plus a small set of Ambarella quirks.

Right, please re-read carefully what he wrote

"This needs to be rewritten using the 8250 library in the kernel
under drivers/tty/serial/8250/8250_ambarella.c
or similar."

You already confirmed that your IP has nothing to do with the Synopsys. Why is
the 8250_dw touched?!

> [1] https://lore.kernel.org/r/CAD++jLm6HzEU1TM-c=Vtjv3FJEBecVP7TyxSgq_Q0zF-YwT6NA@xxxxxxxxxxxxxx/

> -----Original Message-----
> From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> 
> Sent: Friday, August 14, 2026 19:53
> On Fri, Aug 14, 2026 at 09:33:45AM +0000, Long Zhao wrote:
> > From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > Sent: Friday, August 14, 2026 16:56
> > On Thu, Aug 13, 2026 at 06:35:13PM +0800, Long Zhao via B4 Relay wrote:
> > 
> > > Add CV75 platform data with an ETOI IER mask and skip-set-rate so 
> > > the DesignWare 8250 driver can drive the Ambarella UART for console use.
> 
> > Thanks for the review. Agreed the commit message was too brief.

...

> > > +	/* Keep variant-specific bits in the shadow across subsequent 
> > > +updates. */
> > 
> > This says what code is doing. Instead it must say "why?" the code is doing this.
> > 
> > > +	up->ier |= d->pdata->ier_mask;
> > > +	serial_port_out(p, UART_IER, up->ier);
> 
> ...
> 
> > In case there is an HW bug, where can we get the errata, please? (For 
> > a bare minimum add a reference to the Errata document you give to the 
> > customers.)
> 
> > This is not a silicon erratum. The Ambarella UART is not Synopsys 
> > DesignWare IP; it is an Ambarella 8250-compatible UART. We still use 
> > the snps-dw-apb-uart binding / 8250_dw because the programming model 
> > matches closely enough, with two quirks (ETOI IER bit and 
> > SKIP_SET_RATE). I will expand the commit message and rewrite the 
> > comment to explain why in the next revision.
> 
> Okay, what does it make to think that 8250_dw is a suitable choice?
> What are the features that are repetitive would be if you use a custom 8250-based driver (using the generic 8250 code)?

...

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You have to get rid of this trailer. This is last time I reply on messages with
it. (Replying to it might lead to some legal consequences for me and others...)

-- 
With Best Regards,
Andy Shevchenko