netdev - Re: [PATCH 1/2] net: fec: use dma_alloc

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Date:   Fri, 2 Dec 2022 08:02:23 +0100
From:   Christoph Hellwig <hch@....de>
To:     Greg Ungerer <gerg@...ux-m68k.org>
Cc:     Christoph Hellwig <hch@....de>,
        Joakim Zhang <qiangqing.zhang@....com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        linux-m68k@...ts.linux-m68k.org, uclinux-dev@...inux.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] net: fec: use dma_alloc_noncoherent for m532x

On Thu, Dec 01, 2022 at 03:41:34PM +1000, Greg Ungerer wrote:
>>     #ifdef CONFIG_M532x
>> +	/*
>> +	 * Hacky flush of all caches instead of using the DMA API for the TSO
>> +	 * headers.
>> +	 */
>>   	flush_cache_all();
>
> Even with this corrected this will now end up failing on all other ColdFire types
> with the FEC hardware module (all the non-M532x types) once the arch_dma_alloc()
> returns NULL.
>
> Did you mean "ifndef CONFIG_COLDFIRE" here?

How did these work before given that the cache flush is conditional
on CONFIG_M532x?

>> +#else
>> +		/* m68knommu manually flushes all caches in fec_enet_rx_queue */
>> +		txq->tso_hdrs = dma_alloc_noncoherent(&fep->pdev->dev,
>> +					txq->bd.ring_size * TSO_HEADER_SIZE,
>> +					&txq->tso_hdrs_dma, DMA_BIDIRECTIONAL,
>> +					GFP_KERNEL);
>> +#endif
>>   		if (!txq->tso_hdrs) {
>>   			ret = -ENOMEM;
>>   			goto alloc_failed;
>
> And what about the dmam_alloc_coherent() call in fec_enet_init()?
> Does that need changing too?

If that's actually use by the FEC implementations on coldire: yes.
But maybe I need even more help on how the cache flushing is suppoѕed
to actually work here.