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Date:   Thu, 02 Aug 2018 10:35:10 +0200
From:   Stefan Agner <stefan@agner.ch>
To:     Andy Duan <fugang.duan@nxp.com>
Cc:     davem@davemloft.net, krzk@kernel.org, robin.murphy@arm.com,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] net: fec: check DMA addressing limitations
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On 02.08.2018 09:47, Andy Duan wrote:
> From: Stefan Agner <stefan@agner.ch> Sent: 2018年8月2日 15:16
>> On 02.08.2018 04:00, Andy Duan wrote:
>> > From: Stefan Agner <stefan@agner.ch> Sent: 2018年8月1日 19:45
>> >> Check DMA addressing limitations as suggested by the DMA API how-to.
>> >> This does not fix a particular issue seen but is considered good style.
>> >>
>> >> Signed-off-by: Stefan Agner <stefan@agner.ch>
>> >> ---
>> >>  drivers/net/ethernet/freescale/fec_main.c | 6 ++++++
>> >>  1 file changed, 6 insertions(+)
>> >>
>> >> diff --git a/drivers/net/ethernet/freescale/fec_main.c
>> >> b/drivers/net/ethernet/freescale/fec_main.c
>> >> index c729665107f5..af0fb200e936 100644
>> >> --- a/drivers/net/ethernet/freescale/fec_main.c
>> >> +++ b/drivers/net/ethernet/freescale/fec_main.c
>> >> @@ -3146,6 +3146,12 @@ static int fec_enet_init(struct net_device
>> >> *ndev)
>> >>  	fep->tx_align = 0x3;
>> >>  #endif
>> >>
>> >> +	/* Check mask of the streaming and coherent API */
>> >> +	if (dma_set_mask_and_coherent(&fep->pdev->dev,
>> >> DMA_BIT_MASK(32))) {
>> >> +		dev_warn(&fep->pdev->dev, "No suitable DMA
>> available\n");
>> >> +		return -ENODEV;
>> > It is better:
>> >
>> > ret = dma_set_mask_and_coherent(&fep->pdev->dev,
>> DMA_BIT_MASK(32)); if
>> > (ret < 0) {
>> > 	dev_warn(&fep->pdev->dev, "No suitable DMA available\n");
>> > 	return ret;
>> > }
>>
>> The code comes from the example in
>> Documentation/DMA-API-HOWTO.txt.
>>
>> I can rearrange if you prefer.
>>
> It is better to return the real error code like -EIO if dma_mask is
> not initialized.

Good point. Will send a v2.

--
Stefan

> 
>> >
>> >
>> > If the patch aim to "OF: Don't set default coherent DMA mask", I think
>> > not only this driver need to add the DMA mask limitations,  many other
>> > drivers also need.
>>
>> It doesn't exactly address the issue since with that patch DMA mask wasn't
>> set at all. This code would just make the driver fail with -ENODEV instead of
>> -ENOMEM.
>>
> Yes, I agree. It doesn't address the issue if no patch "of/platform:
> Initialise default DMA masks".
> 
> For non-DT, it seems dma_coerce_mask_and_coherent() much better.
> 
>> To force a DMA mask I would have to set the DMA mask using
>> dma_coerce_mask_and_coherent(). But as discussed with Robin it is safe
>> to assume that an initial mask is set by the bus code:
>> https://emea01.safelinks.protection.outlook.com/?url=http%3A%2F%2Flk
>> ml.kernel.org%2Fr%2F892f9d14-e6fd-7b1b-d07b-af0be6e623fa%40arm.c
>> om&amp;data=02%7C01%7Cfugang.duan%40nxp.com%7C618543fb9b4e
>> 4f9fa49908d5f847c47f%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%
>> 7C0%7C636687909487381876&amp;sdata=hyeeh0KSC3Fu7VDl4A8JbcCO
>> %2FwocUpTEMvTv1hjba0E%3D&amp;reserved=0
>>
>> Setting the DMA mask on DT buses has been addressed by Robin with
>> "of/platform: Initialise default DMA masks". So everything should be fine
>> again.
>>
> Anyway, I am fine with the patch except the return code.
> Thanks.
> 
>> I agree, other drivers need fixing too.
>>
>> --
>> Stefan
>>
>> >
>> >
>> >> +	}
>> >> +
>> >>  	fec_enet_alloc_queue(ndev);
>> >>
>> >>  	bd_size = (fep->total_tx_ring_size + fep->total_rx_ring_size) *
>> >> dsize;
>> >> --
>> >> 2.18.0