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

From	David Laight <David.Laight@ACULAB.COM>
Newsgroups	linux.kernel
Subject	RE: [PATCH 4/9] net: moxart: use correct accessors for DMA memory
Date	2016-01-28 13:40 +0100
Message-ID	<qVU1J-3nX-53@gated-at.bofh.it> (permalink)
References	<qVyXg-4EQ-3@gated-at.bofh.it> <qVyXh-4EQ-9@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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

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RE: [PATCH 4/9] net: moxart: use correct accessors for DMA memory David Laight <David.Laight@ACULAB.COM> - 2016-01-28 13:40 +0100
  Re: [PATCH 4/9] net: moxart: use correct accessors for DMA memory Arnd Bergmann <arnd@arndb.de> - 2016-01-28 18:00 +0100
    Re: [PATCH 4/9] net: moxart: use correct accessors for DMA memory Arnd Bergmann <arnd@arndb.de> - 2016-01-28 18:00 +0100

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