netdev - Re: [PATCH/RFC v2 net-next] ravb: unmap descriptors when freeing rings

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Date:   Fri, 13 Jan 2017 13:01:35 +0100
From:   Simon Horman <horms@...ge.net.au>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Cc:     David Miller <davem@...emloft.net>,
        Magnus Damm <magnus.damm@...il.com>, netdev@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH/RFC v2 net-next] ravb: unmap descriptors when freeing
 rings

On Thu, Jan 12, 2017 at 07:33:51PM +0300, Sergei Shtylyov wrote:
> On 01/12/2017 04:18 PM, Simon Horman wrote:
> 
> >...
> >
> >>>>  Here, it stop once an untransmitted buffer is encountered...
> >>>
> >>>Yes, I see that now.
> >>>
> >>>I wonder if we should:
> >>>
> >>>a) paramatise ravb_tx_free() so it may either clear all transmitted buffers
> >>>  (current behaviour) or all buffers (new behaviour).
> >>>b) provide a different version of this loop in ravb_ring_free()
> >>>
> >>>What are your thoughts?
> >>
> >>   I'm voting for (b).
> >
> >Ok, something like this?
> >
> >@@ -215,6 +225,30 @@ static void ravb_ring_free(struct net_device *ndev, int q)
> > 	}
> >
> > 	if (priv->tx_ring[q]) {
> >+		for (; priv->cur_tx[q] - priv->dirty_tx[q] > 0; priv->dirty_tx[q]++) {
> 
>    You're still copying the loop logic from ravb_tx_free() while we (I
> think) need a simple loop over all the descriptor ring.

I thought the above may be better as it seems to me that only descriptors
in the range described above could need to be freed. But simpler may be
better. And I also noticed several other problems with the code I posted
yesterday afternoon.

How about something like this?

@@ -215,6 +225,17 @@ static void ravb_ring_free(struct net_device *ndev, int q)
 	}
 
 	if (priv->tx_ring[q]) {
+		for (i = 0; i < priv->num_tx_ring[q] * NUM_TX_DESC; i++) {
+			struct ravb_tx_desc *desc = &priv->tx_ring[q][i];
+
+			if (desc->die_dt != DT_EEMPTY) {
+				u32 size = le16_to_cpu(desc->ds_tagl) & TX_DS;
+
+				dma_unmap_single(ndev->dev.parent,
+						 le32_to_cpu(desc->dptr),
+						 size, DMA_TO_DEVICE);
+			}
+		}
 		ring_size = sizeof(struct ravb_tx_desc) *
 			    (priv->num_tx_ring[q] * NUM_TX_DESC + 1);
 		dma_free_coherent(ndev->dev.parent, ring_size, priv->tx_ring[q],