netdev - Re: [PATCH 1/3] net: macb: fix random memory corruption on RX with 64-bit DMA

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Message-ID: <96541ac7-7338-3a09-4891-82542a2b3873@microchip.com>
Date:   Thu, 6 Dec 2018 14:16:12 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <davem@...emloft.net>, <anssi.hannula@...wise.fi>
CC:     <Nicolas.Ferre@...rochip.com>, <netdev@...r.kernel.org>,
        <harini.katakam@...inx.com>, <michal.simek@...inx.com>
Subject: Re: [PATCH 1/3] net: macb: fix random memory corruption on RX with
 64-bit DMA



On 05.12.2018 22:32, David Miller wrote:
> From: Anssi Hannula <anssi.hannula@...wise.fi>
> Date: Fri, 30 Nov 2018 20:21:35 +0200
> 
>> @@ -682,6 +682,11 @@ static void macb_set_addr(struct macb *bp, struct macb_dma_desc *desc, dma_addr_
>>  	if (bp->hw_dma_cap & HW_DMA_CAP_64B) {
>>  		desc_64 = macb_64b_desc(bp, desc);
>>  		desc_64->addrh = upper_32_bits(addr);
>> +		/* The low bits of RX address contain the RX_USED bit, clearing
>> +		 * of which allows packet RX. Make sure the high bits are also
>> +		 * visible to HW at that point.
>> +		 */
>> +		dma_wmb();
>>  	}
> 
> I agree with that dma_wmb() is what should be used here.
> 
> We are ordering CPU stores with DMA visibility, which is exactly what
> the dma_*() are for.
> 
> If it doesn't work properly on some architecture's implementation of dma_*(),
> those should be fixed rather than papering over it in the drivers.
> 

Ok, agree. This driver uses rmb()/wmb() all over the place with regards to
DMA descriptors updates, so I tough it might be a reason for that.

Thank you,
Claudiu Beznea