netdev - Re: [PATCH net-next v3 01/12] net: wwan: t7xx: Add control DMA interface

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Date:   Thu, 16 Dec 2021 13:08:55 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Ricardo Martinez <ricardo.martinez@...ux.intel.com>
cc:     Netdev <netdev@...r.kernel.org>, linux-wireless@...r.kernel.org,
        kuba@...nel.org, davem@...emloft.net, johannes@...solutions.net,
        ryazanov.s.a@...il.com, loic.poulain@...aro.org,
        m.chetan.kumar@...el.com, chandrashekar.devegowda@...el.com,
        linuxwwan@...el.com, chiranjeevi.rapolu@...ux.intel.com,
        haijun.liu@...iatek.com, amir.hanania@...el.com,
        andriy.shevchenko@...ux.intel.com, dinesh.sharma@...el.com,
        eliot.lee@...el.com, mika.westerberg@...ux.intel.com,
        moises.veleta@...el.com, pierre-louis.bossart@...el.com,
        muralidharan.sethuraman@...el.com, Soumya.Prakash.Mishra@...el.com,
        sreehari.kancharla@...el.com, suresh.nagaraj@...el.com
Subject: Re: [PATCH net-next v3 01/12] net: wwan: t7xx: Add control DMA
 interface

On Mon, 6 Dec 2021, Ricardo Martinez wrote:

> From: Haijun Liu <haijun.liu@...iatek.com>
> 
> Cross Layer DMA (CLDMA) Hardware interface (HIF) enables the control
> path of Host-Modem data transfers. CLDMA HIF layer provides a common
> interface to the Port Layer.
> 
> CLDMA manages 8 independent RX/TX physical channels with data flow
> control in HW queues. CLDMA uses ring buffers of General Packet
> Descriptors (GPD) for TX/RX. GPDs can represent multiple or single
> data buffers (DB).
> 
> CLDMA HIF initializes GPD rings, registers ISR handlers for CLDMA
> interrupts, and initializes CLDMA HW registers.
> 
> CLDMA TX flow:
> 1. Port Layer write
> 2. Get DB address
> 3. Configure GPD
> 4. Triggering processing via HW register write
> 
> CLDMA RX flow:
> 1. CLDMA HW sends a RX "done" to host
> 2. Driver starts thread to safely read GPD
> 3. DB is sent to Port layer
> 4. Create a new buffer for GPD ring
> 
> Signed-off-by: Haijun Liu <haijun.liu@...iatek.com>
> Signed-off-by: Chandrashekar Devegowda <chandrashekar.devegowda@...el.com>
> Co-developed-by: Ricardo Martinez <ricardo.martinez@...ux.intel.com>
> Signed-off-by: Ricardo Martinez <ricardo.martinez@...ux.intel.com>


> +static struct cldma_request *t7xx_cldma_ring_step_forward(struct cldma_ring *ring,
> +							  struct cldma_request *req)
> +{
> +	if (req->entry.next == &ring->gpd_ring)
> +		return list_first_entry(&ring->gpd_ring, struct cldma_request, entry);
> +
> +	return list_next_entry(req, entry);
> +}
> +
> +static struct cldma_request *t7xx_cldma_ring_step_backward(struct cldma_ring *ring,
> +							   struct cldma_request *req)
> +{
> +	if (req->entry.prev == &ring->gpd_ring)
> +		return list_last_entry(&ring->gpd_ring, struct cldma_request, entry);
> +
> +	return list_prev_entry(req, entry);
> +}

Wouldn't these two seems generic enough to warrant adding something like 
list_next/prev_entry_circular(...) to list.h?

> +static int t7xx_cldma_alloc_and_map_skb(struct cldma_ctrl *md_ctrl, struct cldma_request *req,
> +					size_t size)
> +{
> +	req->skb = __dev_alloc_skb(size, GFP_KERNEL);
> +	if (!req->skb)
> +		return -ENOMEM;
> +
> +	req->mapped_buff = dma_map_single(md_ctrl->dev, req->skb->data,
> +					  t7xx_skb_data_size(req->skb), DMA_FROM_DEVICE);

t7xx_skb_data_size() is not defined by this patch but only in a later 
patch in the series.

Also, I'd prefer its name to be changed to e.g. t7xx_skb_data_area_size() 
given what it calculates. IHMO, "data size" refers to actual 
frame/packet/payload and does not include the reserves/*rooms around it
so the name is bit misleading as is.


-- 
 i.