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

[matthew . gerlach]

On Fri, 21 Oct 2022, Andy Shevchenko wrote:

> On Thu, Oct 20, 2022 at 02:26:09PM -0700, matthew.gerlach@xxxxxxxxxxxxxxx wrote:
> > From: Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>
> >
> > 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?

It can be u64, and I will consider it for the next iteration.
> > +{
> > +	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.

The masking of next below ensures that the offset it at least 4 byte 
aligned, but it might make sense to define the next field in terms of 8 
byte 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

I'll change mmio to MMIO here and a place in the documentation that I 
noticed.

> > +		 * 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().

I will remove the redundant code.

> > +		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?

I agree separate FIELD_GET() calls will be cleaner.

> > +	}
> > +
> > +	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.

That is a good suggestion that should clean up the code 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