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

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Date: Thu, 18 Apr 2024 12:43:25 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Serge Semin <fancer.lancer@...il.com>
Cc: Viresh Kumar <vireshk@...nel.org>, Vinod Koul <vkoul@...nel.org>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>, dmaengine@...r.kernel.org,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] dmaengine: dw: Add peripheral bus width verification

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.

> > > +	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.

-- 
With Best Regards,
Andy Shevchenko