linux-kernel - Re: [PATCH v9 3/4] fpga: dfl: add basic support for DFHv1

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Date:   Mon, 9 Jan 2023 10:04:32 -0800 (PST)
From:   matthew.gerlach@...ux.intel.com
To:     Xu Yilun <yilun.xu@...el.com>
cc:     hao.wu@...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,
        andriy.shevchenko@...ux.intel.com,
        niklas.soderlund+renesas@...natech.se, macro@...am.me.uk,
        johan@...nel.org, lukas@...ner.de, ilpo.jarvinen@...ux.intel.com,
        marpagan@...hat.com, bagasdotme@...il.com
Subject: Re: [PATCH v9 3/4] fpga: dfl: add basic support for DFHv1



On Mon, 9 Jan 2023, Xu Yilun wrote:

> On 2023-01-04 at 15:22:52 -0800, matthew.gerlach@...ux.intel.com wrote:
>> From: Matthew Gerlach <matthew.gerlach@...ux.intel.com>
>>
>> Version 1 of the Device Feature Header (DFH) definition adds
>> functionality to the Device Feature List (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@...ux.intel.com>
>> Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
>>
>
> [...]
>
>> +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;
>> +
>> +		if (FIELD_GET(DFHv1_PARAM_HDR_NEXT_EOP, v))
>> +			break;
>> +
>> +		next = FIELD_GET(DFHv1_PARAM_HDR_NEXT_OFFSET, v);
>> +		params += next;
>> +	}
>> +
>> +	return NULL;
>> +}
>> +
>> +/**
>> + * dfh_find_param() - find parameter block for the given parameter id
>> + * @dfl_dev: dfl device
>> + * @param_id: id of dfl parameter
>> + * @pcount: destination to store size of parameter data in u64 bit words
>
> As I mentioned before, could the size of the parameter data just be number
> of bytes? This is the most common way for a data block.

returning a void* and a size_t in bytes would be more consistent.  I will 
make your suggested change.

Thanks,
Matthew Gerlach

>
> Thanks,
> Yilun
>
>> + *
>> + * Return: pointer to start of parameter data, PTR_ERR otherwise.
>> + */
>> +void *dfh_find_param(struct dfl_device *dfl_dev, int param_id, size_t *pcount)
>> +{
>> +	u64 *phdr = find_param(dfl_dev->params, dfl_dev->param_size, param_id);
>> +
>> +	if (!phdr)
>> +		return ERR_PTR(-ENOENT);
>> +
>> +	if (pcount)
>> +		*pcount = FIELD_GET(DFHv1_PARAM_HDR_NEXT_OFFSET, *phdr) - 1;
>> +
>> +	return phdr + 1;
>> +}
>> +EXPORT_SYMBOL_GPL(dfh_find_param);
>