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Subject: Re: [PATCH] staging: comedi: s626: Remove pci-dma-compat wrapper
 APIs.
To:     Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
        Suraj Upadhyay <usuraj35@gmail.com>,
        gregkh@linuxfoundation.org, hsweeten@visionengravers.com
Cc:     linux-kernel@vger.kernel.org, devel@driverdev.osuosl.org,
        kernel-janitors@vger.kernel.org
References: <20200711123533.GA15038@blackclown>
 <6f701731-d0af-1bd5-5854-42f0ba39ed35@wanadoo.fr>
From:   Ian Abbott <abbotti@mev.co.uk>
Organization: MEV Ltd.
Message-ID: <3747ce02-feb3-359f-c60d-233e412c6062@mev.co.uk>
Date:   Mon, 13 Jul 2020 14:48:41 +0100
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On 11/07/2020 14:38, Christophe JAILLET wrote:
> Le 11/07/2020 ? 14:35, Suraj Upadhyay a ?crit?:
>> The legacy API wrappers in include/linux/pci-dma-compat.h
>> should go away as it creates unnecessary midlayering
>> for include/linux/dma-mapping.h APIs, instead use dma-mapping.h
>> APIs directly.
>>
>> The patch has been generated with the coccinelle script below
>> and compile-tested.
>>
>> [...]
>> @@ expression E1, E2, E3; @@
>> - pci_alloc_consistent(E1, E2, E3)
>> + dma_alloc_coherent(&E1->dev, E2, E3, GFP_ATOMIC)
>>
>> @@ expression E1, E2, E3; @@
>> - pci_zalloc_consistent(E1, E2, E3)
>> + dma_alloc_coherent(&E1->dev, E2, E3, GFP_ATOMIC)
> 
> This is the tricky part of this kind of cleanup, see below.
> 
> GFP_ATOMIC can't be wrong because it is was exactly what was done with 
> the pci_ function.
> However, most of the time, it can safely be replaced by GFP_KERNEL which 
> gives more opportunities to the memory allocator.
> 
>> [...]
>> diff --git a/drivers/staging/comedi/drivers/s626.c 
>> b/drivers/staging/comedi/drivers/s626.c
>> index 084a8e7b9fc2..c159416662fd 100644
>> --- a/drivers/staging/comedi/drivers/s626.c
>> +++ b/drivers/staging/comedi/drivers/s626.c
>> @@ -2130,13 +2130,15 @@ static int s626_allocate_dma_buffers(struct 
>> comedi_device *dev)
>> ????? void *addr;
>> ????? dma_addr_t appdma;
>> -??? addr = pci_alloc_consistent(pcidev, S626_DMABUF_SIZE, &appdma);
>> +??? addr = dma_alloc_coherent(&pcidev->dev, S626_DMABUF_SIZE, &appdma,
>> +????????????????? GFP_ATOMIC);
>> ????? if (!addr)
>> ????????? return -ENOMEM;
>> ????? devpriv->ana_buf.logical_base = addr;
>> ????? devpriv->ana_buf.physical_base = appdma;
>> -??? addr = pci_alloc_consistent(pcidev, S626_DMABUF_SIZE, &appdma);
>> +??? addr = dma_alloc_coherent(&pcidev->dev, S626_DMABUF_SIZE, &appdma,
>> +????????????????? GFP_ATOMIC);
>> ????? if (!addr)
>> ????????? return -ENOMEM;
>> ????? devpriv->rps_buf.logical_base = addr;
> 's626_allocate_dma_buffers()' is only called from 's626_auto_attach()'.
> In this function, around the call to 's626_allocate_dma_buffers()', you 
> can see:
>  ? - a few lines before, a call to 'comedi_alloc_devpriv()'
> 
>  ? - a few lines after, a call to 'comedi_alloc_subdevices()'
> 
> These 2 functions make some memory allocation using GFP_KERNEL.
> 
> So it is likely that using GFP_KERNEL in your proposal is also valid.

Indeed, GFP_KERNEL is perfectly fine here.  It could be done as a 
follow-up patch, or done in a v2 of this patch with a mention in the 
patch description.

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