netdev - RE: [PATCH 4/9] net: moxart: use correct accessors for DMA memory

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Date:	Thu, 28 Jan 2016 12:36:19 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Arnd Bergmann' <arnd@...db.de>,
	"David S. Miller" <davem@...emloft.net>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	françois romieu <romieu@...zoreil.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 4/9] net: moxart: use correct accessors for DMA memory

From: Arnd Bergmann
> Sent: 27 January 2016 14:05
> The moxart ethernet driver confuses coherent DMA buffers with
> MMIO registers.
> 
> moxart_ether.c: In function 'moxart_mac_setup_desc_ring':
> moxart_ether.c:146:428: error: passing argument 1 of '__fswab32' makes integer from pointer without a
> cast [-Werror=int-conversion]
> moxart_ether.c:74:39: warning: incorrect type in argument 3 (different address spaces)
> moxart_ether.c:74:39:    expected void *cpu_addr
> moxart_ether.c:74:39:    got void [noderef] <asn:2>*tx_desc_base
> 
> This leaves the basic logic alone and uses normal pointers for
> the virtual address of the descriptor. As we cannot use readl/writel
> to access them, we also introduce our own moxart_desc_read
> moxart_desc_write helpers that perform the same endianess swap
> as the original code, but without the extra barriers and address
> space conversion.

I'm pretty sure you need to add some explicit barriers:

> @@ -354,8 +364,8 @@ static int moxart_mac_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  	txdes1 = TX_DESC1_LTS | TX_DESC1_FTS | (len & TX_DESC1_BUF_SIZE_MASK);
>  	if (tx_head == TX_DESC_NUM_MASK)
>  		txdes1 |= TX_DESC1_END;
> -	writel(txdes1, desc + TX_REG_OFFSET_DESC1);
> -	writel(TX_DESC0_DMA_OWN, desc + TX_REG_OFFSET_DESC0);
> +	moxart_desc_write(txdes1, desc + TX_REG_OFFSET_DESC1);
> +	moxart_desc_write(TX_DESC0_DMA_OWN, desc + TX_REG_OFFSET_DESC0);

Those last two writes must happen in that order.
There may be others.

	David