linux-kernel - Re: [PATCH v4 3/4] fpga: dfl: add basic support DFHv1

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Message-ID: <Y1HGhT5+Nxv6anw5@smile.fi.intel.com>
Date:   Fri, 21 Oct 2022 01:07:01 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     matthew.gerlach@...ux.intel.com
Cc:     hao.wu@...el.com, yilun.xu@...el.com, russell.h.weight@...el.com,
        basheer.ahmed.muddebihal@...el.com, trix@...hat.com,
        mdf@...nel.org, linux-fpga@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        tianfei.zhang@...el.com, corbet@....net,
        gregkh@...uxfoundation.org, linux-serial@...r.kernel.org,
        jirislaby@...nel.org, geert+renesas@...der.be,
        niklas.soderlund+renesas@...natech.se, macro@...am.me.uk,
        johan@...nel.org, lukas@...ner.de, ilpo.jarvinen@...ux.intel.com,
        marpagan@...hat.com
Subject: Re: [PATCH v4 3/4] fpga: dfl: add basic support DFHv1

On Thu, Oct 20, 2022 at 02:26:09PM -0700, matthew.gerlach@...ux.intel.com wrote:
> From: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
> 
> Add generic support for MSI-X interrupts for DFL devices.
> 
> The location of a feature's registers is explicitly
> described in DFHv1 and can be relative to the base of the DFHv1
> or an absolute address.  Parse the location and pass the information
> to DFL driver.

...

> +static void *find_param(void *base, resource_size_t max, int param)

Why base can't be u64 * to begin with?

> +{
> +	int off = 0;
> +	u64 v, next;
> +
> +	while (off < max) {

Maybe you need a comment somewhere to tell that the caller guarantees that max
won't provoke OOB accesses.

> +		v = *(u64 *)(base + off);

Okay, if offset is not multiple of at least 4, how do you guarantee no
exception on the architectures with disallowed misaligned accesses?

Making base to be u64 * solves this, but you need to take care to provide
offset in terms of u64 words.

> +		if (param == FIELD_GET(DFHv1_PARAM_HDR_ID, v))
> +			return base + off + DFHv1_PARAM_DATA;
> +
> +		next = FIELD_GET(DFHv1_PARAM_HDR_NEXT_OFFSET, v);
> +		off += next & ~DFHv1_PARAM_HDR_NEXT_MASK;
> +		if (next & DFHv1_PARAM_HDR_NEXT_EOL)
> +			break;
> +
> +	}
> +
> +	return NULL;
> +}

...

> +		/*
> +		 * DFHv0 only provides mmio resource information for each feature

MMIO

> +		 * in the DFL header.  There is no generic interrupt information.
> +		 * Instead, features with interrupt functionality provide
> +		 * the information in feature specific registers.
> +		 */

...

> +		if (!finfo->param_size)
>  			break;

This is redundant as it's implied by find_param().

> +		p = find_param(params, finfo->param_size, DFHv1_PARAM_ID_MSI_X);
> +		if (!p)
>  			break;

...

> +static int dfh_get_psize(void __iomem *dfh_base, resource_size_t max)
> +{
> +	int size = 0;
> +	u64 v, next;
> +
> +	if (!FIELD_GET(DFHv1_CSR_SIZE_GRP_HAS_PARAMS,
> +		       readq(dfh_base + DFHv1_CSR_SIZE_GRP)))
> +		return 0;
> +
> +	while (size + DFHv1_PARAM_HDR < max) {
> +		v = readq(dfh_base + DFHv1_PARAM_HDR + size);
> +
> +		next = FIELD_GET(DFHv1_PARAM_HDR_NEXT_OFFSET, v);
> +		if (!(next & ~DFHv1_PARAM_HDR_NEXT_MASK))
> +			return -EINVAL;
> +
> +		size += next & ~DFHv1_PARAM_HDR_NEXT_MASK;
> +
> +		if (next & DFHv1_PARAM_HDR_NEXT_EOL)
> +			return size;

These 3 looks like they deserve different fields and hence separate FIELD_GET()
will return exactly what we need without additional masking, right?

> +	}
> +
> +	return -ENOENT;
> +}

...

> +	if (dfh_psize > 0) {

Isn't this implied by memcpy_fromio()? I mean if it's 0, nothing bad will
happen if you call the above directly.

> +		memcpy_fromio(finfo->params,
> +			      binfo->ioaddr + ofst + DFHv1_PARAM_HDR, dfh_psize);
> +		finfo->param_size = dfh_psize;
> +	}

...

>  	finfo->mmio_res.flags = IORESOURCE_MEM;
> +	if (dfh_ver == 1) {
> +		v = readq(binfo->ioaddr + ofst + DFHv1_CSR_ADDR);
> +		if (v & DFHv1_CSR_ADDR_REL)
> +			finfo->mmio_res.start = v & ~DFHv1_CSR_ADDR_REL;
> +		else
> +			finfo->mmio_res.start = binfo->start + ofst +
> +					       FIELD_GET(DFHv1_CSR_ADDR_MASK, v);
> +
> +		v = readq(binfo->ioaddr + ofst + DFHv1_CSR_SIZE_GRP);
> +		finfo->mmio_res.end = finfo->mmio_res.start +
> +				      FIELD_GET(DFHv1_CSR_SIZE_GRP_SIZE, v) - 1;
> +	} else {
> +		finfo->mmio_res.start = binfo->start + ofst;
> +		finfo->mmio_res.end = finfo->mmio_res.start + size - 1;
> +	}

You may define

	resource_size_t start, end;

locally and simplify above quite a bit.

...

> +void *dfh_find_param(struct dfl_device *dfl_dev, int param);

+ Blank line.

>  #endif /* __LINUX_DFL_H */

-- 
With Best Regards,
Andy Shevchenko