Re: [PATCH net v2 0/3] Limit devicetree parameters to hardware capability

[Kunihiko Hayashi]

Hi Russell,

On 2025/01/24 1:31, Russell King (Oracle) wrote:
> On Thu, Jan 23, 2025 at 02:25:15PM +0900, Kunihiko Hayashi wrote:
> > Hi Russell,
> >
> > Thank you for your comment.
> >
> > On 2025/01/21 19:25, Russell King (Oracle) wrote:
> > > On Tue, Jan 21, 2025 at 01:41:35PM +0900, Kunihiko Hayashi wrote:
> > > > This series includes patches that checks the devicetree properties,
> > > > the number of MTL queues and FIFO size values, and if these
> specified
> > > > values exceed the value contained in the hardware capabilities,
> limit to
> > > > the values from the capabilities.
> > > >
> > > > And this sets hardware capability values if FIFO sizes are not
> specified
> > > > and removes redundant lines.
> > >
> > > I think you also indeed to explain why (and possibly understand) - if
> > > there are hardware capabilities that describe these parameters - it
> has
> > > been necessary to have them in firmware as well.
> > >
> > > There are two scenarios I can think of why these would be duplicated:
> > >
> > > 1. firmware/platform capabilities are there to correct wrong values
> > >      provided by the hardware.
> > > 2. firmware/platform capabilities are there to reduce the parameters
> > >      below hardware maximums.
> > >
> > > Which it is affects whether your patch is correct or not, and thus
> needs
> > > to be mentioned.
> >
> > I think scenario 2 applies in this case.
>
> In light of my other reply
> (https://lore.kernel.org/r/Z4_ZilVFKacuAUE8@xxxxxxxxxxxxxxxxxxxxx) I
> don't think either of my two above applies, and the driver is designed
> to allow platform code to override the hardware value, or to provide
> the value if there is no hardware value.

I understand. Especially I realized that I had to care about some hardwares
not having these values.

> My suggestion, therefore, would be (e.g.):
>
> 	if (priv->dma_cap.rx_fifo_size &&
> 	    priv->plat->rx_fifo_size > priv->dma_cap.rx_fifo_size) {
> 		dev_warn(priv->device,
> 			 "Rx FIFO size exceeds dma capability (%d)\n",
> 			 priv->plat->rx_fifo_size);
> 		priv->plat->rx_fifo_size = priv->dma_cap.rx_fifo_size;
> 	}
>
> if we still want to limit it to the hardware provided capability, where
> that is provided.

Thank you for your suggestion. I also came up with the same code in:
https://lore.kernel.org/all/c2aa354d-1bd5-4fb0-aa8b8-48fcce3c1628@xxxxxxxxxxxxx/#t

I'll reflect this code to the next.

Thank you,

---
Best Regards
Kunihiko Hayashi