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


On Wed, 21 Dec 2022, Ilpo Järvinen wrote:

> On Tue, 20 Dec 2022, matthew.gerlach@linux.intel.com wrote:
>
>> From: Matthew Gerlach <matthew.gerlach@linux.intel.com>
>>
>> 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@linux.intel.com>
>> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
>> ---
>> 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.
>
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