Re: [PATCH 01/19] bus/cdx: add the cdx bus driver

From: Greg KH <gregkh@linuxfoundation.org>
To: Nipun Gupta <nipun.gupta@amd.com>
Cc: robh+dt@kernel.org, krzysztof.kozlowski+dt@linaro.org,
	rafael@kernel.org, eric.auger@redhat.com,
	alex.williamson@redhat.com, cohuck@redhat.com,
	song.bao.hua@hisilicon.com, mchehab+huawei@kernel.org,
	maz@kernel.org, f.fainelli@gmail.com, jeffrey.l.hugo@gmail.com,
	saravanak@google.com, Michael.Srba@seznam.cz, mani@kernel.org,
	yishaih@nvidia.com, jgg@ziepe.ca, jgg@nvidia.com,
	robin.murphy@arm.com, will@kernel.org, joro@8bytes.org,
	masahiroy@kernel.org, ndesaulniers@google.com,
	linux-arm-kernel@lists.infradead.org,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
	devicetree@vger.kernel.org, okaya@kernel.org,
	harpreet.anand@amd.com, nikhil.agarwal@amd.com,
	michal.simek@amd.com, git@amd.com
Subject: Re: [PATCH 01/19] bus/cdx: add the cdx bus driver
Date: Tue, 17 Jan 2023 15:07:02 +0100	[thread overview]
Message-ID: <Y8arhmVo7LPLuxqr@kroah.com> (raw)
In-Reply-To: <20230117134139.1298-2-nipun.gupta@amd.com>

On Tue, Jan 17, 2023 at 07:11:33PM +0530, Nipun Gupta wrote:
> Introduce AMD CDX bus, which provides a mechanism for scanning
> and probing CDX devices. These devices are memory mapped on
> system bus for Application Processors(APUs).
> 
> CDX devices can be changed dynamically in the Fabric and CDX
> bus interacts with CDX controller to rescan the bus and
> rediscover the devices.
> 
> Signed-off-by: Nipun Gupta <nipun.gupta@amd.com>
> Signed-off-by: Tarak Reddy <tarak.reddy@amd.com>

First off, very nice job, I didn't find any obvious issues with this
integration into the driver core.

That being said, why do you want this in drivers/bus/?  Why not
drivers/cdx/ ?

One minor comment to make the code smaller:

> +static int get_free_index(void)
> +{
> +	unsigned long id_map;
> +	unsigned long mask;
> +	int index = 0;
> +
> +	mask  = (1UL << MAX_CDX_CONTROLLERS) - 1;
> +retry:
> +	id_map = cdx_controller_id_map[0];
> +	if ((id_map & mask) == mask)
> +		return -ENOSPC;
> +
> +	index = ffz(id_map);
> +	if (index >= MAX_CDX_CONTROLLERS)
> +		return -ENOSPC;
> +
> +	if (test_and_set_bit(index, &cdx_controller_id_map[0]))
> +		goto retry;
> +
> +	return index;
> +}

Why not just use the idr/ida structure instead?  That will handle all of
that logic for you and get rid of your bit twiddling.

> +/**
> + * struct cdx_dev_params - CDX device parameters
> + * @cdx: CDX controller associated with the device
> + * @parent: Associated CDX controller
> + * @vendor: Vendor ID for CDX device
> + * @device: Device ID for CDX device
> + * @bus_num: Bus number for this CDX device
> + * @dev_num: Device number for this device
> + * @res: array of MMIO region entries
> + * @res_count: number of valid MMIO regions
> + * @req_id: Requestor ID associated with CDX device
> + */
> +struct cdx_dev_params {
> +	struct cdx_controller *cdx;
> +	u16 vendor;
> +	u16 device;

Are these in little endian format in memory?  Or native?  Or something
else?

thanks,

greg k-h