Re: [PATCH v7 3/4] fpga: dfl: add basic support for DFHv1

[matthew . gerlach]

On Wed, 21 Dec 2022, Ilpo Järvinen wrote:

> On Tue, 20 Dec 2022, matthew.gerlach@xxxxxxxxxxxxxxx wrote:
>
> > From: Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>
> >
> > Version 1 of the Device Feature Header (DFH) definition adds
> > functionality to the DFL bus.
> >
> > A DFHv1 header may have one or more parameter blocks that
> > further describes the HW to SW.  Add support to the DFL bus
> > to parse the MSI-X parameter.
> >
> > The location of a feature's register set 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.
> >
> > Signed-off-by: Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>
> > Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
> > ---
> > v7: no change
> >
> > v6: move MSI_X parameter definitions to drivers/fpga/dfl.h
> >
> > v5: update field names
> >     fix find_param/dfh_get_psize
> >     clean up mmio_res assignments
> >     use u64* instead of void*
> >     use FIELD_GET instead of masking
> >
> > v4: s/MSIX/MSI_X
> >     move kernel doc to implementation
> >     use structure assignment
> >     fix decode of absolute address
> >     clean up comment in parse_feature_irqs
> >     remove use of csr_res
> >
> > v3: remove unneeded blank line
> >     use clearer variable name
> >     pass finfo into parse_feature_irqs()
> >     refactor code for better indentation
> >     use switch statement for irq parsing
> >     squash in code parsing register location
> >
> > v2: fix kernel doc
> >     clarify use of DFH_VERSION field
> > ---
>
> > +static u64 *find_param(u64 *params, resource_size_t max, int param_id)
> > +{
> > +	u64 *end = params + max / sizeof(u64);
> > +	u64 v, next;
> > +
> > +	while (params < end) {
> > +		v = *params;
> > +		if (param_id == FIELD_GET(DFHv1_PARAM_HDR_ID, v))
> > +			return params;
> > +
> > +		next = FIELD_GET(DFHv1_PARAM_HDR_NEXT_OFFSET, v);
> > +		params += next;
> > +		if (FIELD_GET(DFHv1_PARAM_HDR_NEXT_EOP, v))
> > +			break;
> > +	}
> > +
> > +	return NULL;
> > +}
> > +
> > +/**
> > + * dfh_find_param() - find data for the given parameter id
> > + * @dfl_dev: dfl device
> > + * @param: id of dfl parameter
> > + *
> > + * Return: pointer to parameter header on success, NULL otherwise.
> > + */
> > +u64 *dfh_find_param(struct dfl_device *dfl_dev, int param_id)
> > +{
> > +	return find_param(dfl_dev->params, dfl_dev->param_size, param_id);
> > +}
> > +EXPORT_SYMBOL_GPL(dfh_find_param);
>
> BTW, should there be a way for the caller to ensure the parameter is long
> enough?

The caller can look at the DFHv1_PARAM_HDR_NEXT_OFFSET field of the 
parameter header to see the size of the parameter block (header plus 
data).

> All callers probably want to ensure the length of the parameter is valid
> so it would perhaps make sense to add a parameter for the required
> (minimum) length?

Yes, all callers should ensure that the length of the parameter is valid. 
I will add another API call that performs length checking.

Thanks for the feedback,
Matthew Gerlach

> --
> i.