Re: [PATCH net-next v4 02/13] net: wwan: t7xx: Add control DMA interface

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Thu, 13 Jan 2022, Ricardo Martinez wrote:

> From: Haijun Liu <haijun.liu@mediatek.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@mediatek.com>
> Signed-off-by: Chandrashekar Devegowda <chandrashekar.devegowda@intel.com>
> Co-developed-by: Ricardo Martinez <ricardo.martinez@linux.intel.com>
> Signed-off-by: Ricardo Martinez <ricardo.martinez@linux.intel.com>
> ---

> +	struct cldma_ring *tr_ring;
> +	struct cldma_request *tr_done;
> +	struct cldma_request *rx_refill;
> +	struct cldma_request *tx_xmit;
> +	int budget;			/* Same as ring buffer size by default */
> +	spinlock_t ring_lock;

I couldn't figure out what ring_lock is supposed to protect exactly.
Since there were tr_ring operations done w/o ring_lock (in 
t7xx_cldma_gpd_rx_from_q), I was left to wonder whether it's due to
a locking bug or me not understanding what ring_lock is supposed to 
protect.


-- 
 i.