linux-kernel - Re: [PATCH v4 1/3] USB: use genalloc for USB HCs with local memory

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Date:   Tue, 21 May 2019 11:04:12 +0000
From:   Laurentiu Tudor <laurentiu.tudor@....com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "hch@....de" <hch@....de>,
        "stern@...land.harvard.edu" <stern@...land.harvard.edu>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "marex@...x.de" <marex@...x.de>, Leo Li <leoyang.li@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "noring@...rew.org" <noring@...rew.org>,
        "JuergenUrban@....de" <JuergenUrban@....de>
Subject: Re: [PATCH v4 1/3] USB: use genalloc for USB HCs with local memory



On 21.05.2019 11:16, Greg KH wrote:
> On Thu, May 16, 2019 at 02:47:19PM +0300, laurentiu.tudor@....com wrote:
>> From: Laurentiu Tudor <laurentiu.tudor@....com>
>>
>> For HCs that have local memory, replace the current DMA API usage
>> with a genalloc generic allocator to manage the mappings for these
>> devices.
>> This is in preparation for dropping the existing "coherent" dma
>> mem declaration APIs. Current implementation was relying on a short
>> circuit in the DMA API that in the end, was acting as an allocator
>> for these type of devices.
>>
>> For context, see thread here: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flkml.org%2Flkml%2F2019%2F4%2F22%2F357&amp;data=02%7C01%7Claurentiu.tudor%40nxp.com%7Cf5242fb28d154ff9653208d6ddc4b41c%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C636940234237524499&amp;sdata=KEEUP1KH%2BaraWcVKogeYBzrauh%2FFTzGjSxjk%2BuNozjA%3D&amp;reserved=0
>>
>> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@....com>
>> ---
>>   drivers/usb/core/buffer.c   | 15 +++++++++++----
>>   drivers/usb/host/ohci-hcd.c | 23 ++++++++++++++++++-----
>>   include/linux/usb/hcd.h     |  3 +++
>>   3 files changed, 32 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/usb/core/buffer.c b/drivers/usb/core/buffer.c
>> index f641342cdec0..22a8f3f5679b 100644
>> --- a/drivers/usb/core/buffer.c
>> +++ b/drivers/usb/core/buffer.c
>> @@ -16,6 +16,7 @@
>>   #include <linux/io.h>
>>   #include <linux/dma-mapping.h>
>>   #include <linux/dmapool.h>
>> +#include <linux/genalloc.h>
>>   #include <linux/usb.h>
>>   #include <linux/usb/hcd.h>
>>   
>> @@ -124,10 +125,12 @@ void *hcd_buffer_alloc(
>>   	if (size == 0)
>>   		return NULL;
>>   
>> +	if (hcd->driver->flags & HCD_LOCAL_MEM)
>> +		return gen_pool_dma_alloc(hcd->localmem_pool, size, dma);
> 
> Does this patch now break things?  hcd->localmem_pool at this point in
> time is NULL, so this call will fail.  There's no chance for any host
> controller driver to actually set up this pool in this patch, so is
> bisection broken?

Unfortunately, yes. I could lump the patches together but I think 
Christoph suggestion is much better.

> I think you fix this up in later patches, right?

Correct. The last 2 patches update the driver.

> And if so, why do we even need HCD_LOCAL_MEM anymore?  Can't we just
> test for the presence of hcd->localmem_pool in order to determine which
> allocation method to use?

Sure. There are a few more places that need updates but no big deal.

---
Best Regards, Laurentiu