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

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Date:   Mon, 9 Jan 2023 14:44:37 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     matthew.gerlach@...ux.intel.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 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.

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);