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

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Date:   Mon, 24 Oct 2022 07:56:11 -0700 (PDT)
From:   matthew.gerlach@...ux.intel.com
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
cc:     hao.wu@...el.com, yilun.xu@...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,
        niklas.soderlund+renesas@...natech.se, macro@...am.me.uk,
        johan@...nel.org, lukas@...ner.de, ilpo.jarvinen@...ux.intel.com,
        marpagan@...hat.com
Subject: Re: [PATCH v4 3/4] fpga: dfl: add basic support DFHv1



On Fri, 21 Oct 2022, Andy Shevchenko wrote:

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