Re: [PATCH 1/4] dmaengine: dw: Add peripheral bus width verification

[Serge Semin]

On Thu, Apr 18, 2024 at 12:43:25PM +0300, Andy Shevchenko wrote:
> On Wed, Apr 17, 2024 at 10:54:42PM +0300, Serge Semin wrote:
> > On Tue, Apr 16, 2024 at 09:00:50PM +0300, Andy Shevchenko wrote:
> > > On Tue, Apr 16, 2024 at 07:28:55PM +0300, Serge Semin wrote:
> 
> ...
> 
> > > > +	if (reg_width == DMA_SLAVE_BUSWIDTH_UNDEFINED)
> > > > +		reg_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> > > > +	else if (!is_power_of_2(reg_width) || reg_width > max_width)
> > > > +		return -EINVAL;
> > > > +	else /* bus width is valid */
> > > > +		return 0;
> > > > +
> > > > +	/* Update undefined addr width value */
> > > > +	if (dwc->dma_sconfig.direction == DMA_MEM_TO_DEV)
> > > > +		dwc->dma_sconfig.dst_addr_width = reg_width;
> > > > +	else /* DMA_DEV_TO_MEM */
> > > > +		dwc->dma_sconfig.src_addr_width = reg_width;
> > > 
> > 
> > > So, can't you simply call clamp() for both fields in dwc_config()?
> > 
> > Alas I can't. Because the addr-width is the non-memory peripheral
> > setting. We can't change it since the client drivers calculate it on
> > the application-specific basis (CSR widths, transfer length, etc). So
> > we must make sure that the specified value is supported.
> 
> What I meant is to convert this "update" part to the clamping, so
> we will have the check as the above like
> 
> _verify_()
> {
> 	if (reg_width == DMA_SLAVE_BUSWIDTH_UNDEFINED)
> 		return -E...;
> 	if (!is_power_of_2(reg_width) || reg_width > max_width)
> 		return -EINVAL;
> 
> 	/* bus width is valid */
> 	return 0;
> }
> 
> dwc_config()
> {
> 	err = ...
> 	if (err = ...)
> 		clamp?
> 	else if (err)
> 		return err;
> }
> 
> But it's up to you to choose the better variant. I just share the idea.

Ok. Thanks for the suggestion. But I'll stick to my solution then. The
specified *_addr_width values can't/shouldn't be clamped anyway and
having a single verification function will comply to what will be
implemented for the rest of the dwc_onfig() parts in this patchset.

> 
> > > > +	return 0;
> > > > +}
> 
> ...
> 
> > > > +	int err;
> > 
> > > Hmm... we have two functions one of which is using different name for this.
> > 
> > Right, the driver uses both variants (see of.c, platform.c, pci.c too).
> > 
> > > Can we have a patch to convert to err the other one?
> > 
> > To be honest I'd prefer to use the "ret" name instead. It better
> > describes the variable usage context (Although the statements like "if
> > (err) ..." look a bit more readable). So I'd rather convert the "err"
> > vars to "ret". What do you think?
> 

> I'm fine with any choice, just my point is to get it consistent across
> the driver.

Ok. "ret" it is then.

-Serge(y)

> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>