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From: "Andrew F. Davis" <afd@ti.com>
To: Jonathan Cameron <jic23@kernel.org>,
	Hartmut Knaack <knaack.h@gmx.de>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Peter Meerwald <pmeerw@pmeerw.net>, Dan Murphy <dmurphy@ti.com>,
	Rob Herring <robh+dt@kernel.org>, Pawel Moll <pawel.moll@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Kumar Gala <galak@codeaurora.org>
Cc: <linux-iio@vger.kernel.org>, <linux-api@vger.kernel.org>,
	<devicetree@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v4 4/4] iio: health: Add driver for the TI AFE4403 heart monitor
Date: Tue, 2 Feb 2016 11:38:09 -0600	[thread overview]
Message-ID: <56B0E981.5040203@ti.com> (raw)
In-Reply-To: <56ACD24E.3050308@kernel.org>

On 01/30/2016 09:10 AM, Jonathan Cameron wrote:
> On 25/01/16 17:29, Andrew F. Davis wrote:
>> +
>> +static int afe4403_read(struct afe4403_data *afe, unsigned int reg, u32 *val)
>> +{
>> +	u8 tx[4] ____cacheline_aligned = {AFE440X_CONTROL0, 0x0, 0x0,
>> +					  AFE440X_CONTROL0_READ};
> hmm. Can you do this on the stack?  Don't think so but maybe I'm wrong..
> The cachline aligned trick relies on the start of the allocation on the
> heap being aligned and then pads to ensure that the element so tagged
> is also aligned appropriately.

I am not sure ether, I think I borrowed this from some example that did
it like this, but I can't find it now. So, I'll change this to be safe.

>> +	u8 rx[3];
>> +	int ret;
> Even if this were possible, ret is in the same cacheline as tx and rx so
> chaos may well occur.
>
> If you really want to avoid having allocations elsewhere, just use
> spi_write_then_read(afe->spi, tx, 4, NULL, 0) and you should be fine
> as spi_write_then_read uses safe bounce buffers.

spi_write_then_read performs a memcpy to the rx buffer, even though
the length is 0 I believe it is still technically undefined behavior,
but it doesn't seem to cause any issues with the current implementation
so I'll do this.

Thanks,
Andrew

WARNING: multiple messages have this Message-ID (diff)
From: "Andrew F. Davis" <afd-l0cyMroinI0@public.gmane.org>
To: Jonathan Cameron <jic23-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Hartmut Knaack <knaack.h-Mmb7MZpHnFY@public.gmane.org>,
	Lars-Peter Clausen <lars-Qo5EllUWu/uELgA04lAiVw@public.gmane.org>,
	Peter Meerwald <pmeerw-jW+XmwGofnusTnJN9+BGXg@public.gmane.org>,
	Dan Murphy <dmurphy-l0cyMroinI0@public.gmane.org>,
	Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Pawel Moll <pawel.moll-5wv7dgnIgG8@public.gmane.org>,
	Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
	Ian Campbell
	<ijc+devicetree-KcIKpvwj1kUDXYZnReoRVg@public.gmane.org>,
	Kumar Gala <galak-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
Cc: linux-iio-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH v4 4/4] iio: health: Add driver for the TI AFE4403 heart monitor
Date: Tue, 2 Feb 2016 11:38:09 -0600	[thread overview]
Message-ID: <56B0E981.5040203@ti.com> (raw)
In-Reply-To: <56ACD24E.3050308-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>

On 01/30/2016 09:10 AM, Jonathan Cameron wrote:
> On 25/01/16 17:29, Andrew F. Davis wrote:
>> +
>> +static int afe4403_read(struct afe4403_data *afe, unsigned int reg, u32 *val)
>> +{
>> +	u8 tx[4] ____cacheline_aligned = {AFE440X_CONTROL0, 0x0, 0x0,
>> +					  AFE440X_CONTROL0_READ};
> hmm. Can you do this on the stack?  Don't think so but maybe I'm wrong..
> The cachline aligned trick relies on the start of the allocation on the
> heap being aligned and then pads to ensure that the element so tagged
> is also aligned appropriately.

I am not sure ether, I think I borrowed this from some example that did
it like this, but I can't find it now. So, I'll change this to be safe.

>> +	u8 rx[3];
>> +	int ret;
> Even if this were possible, ret is in the same cacheline as tx and rx so
> chaos may well occur.
>
> If you really want to avoid having allocations elsewhere, just use
> spi_write_then_read(afe->spi, tx, 4, NULL, 0) and you should be fine
> as spi_write_then_read uses safe bounce buffers.

spi_write_then_read performs a memcpy to the rx buffer, even though
the length is 0 I believe it is still technically undefined behavior,
but it doesn't seem to cause any issues with the current implementation
so I'll do this.

Thanks,
Andrew

  reply	other threads:[~2016-02-02 17:38 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-01-25 17:28 [PATCH v4 0/4] iio: AFE4404 Heart Rate Monitor and Bio-Sensing Andrew F. Davis
2016-01-25 17:28 ` Andrew F. Davis
2016-01-25 17:28 ` [PATCH v4 1/4] Documentation: afe4404: Add DT bindings for the AFE4404 heart monitor Andrew F. Davis
2016-01-25 17:28   ` Andrew F. Davis
2016-01-25 20:06   ` Peter Meerwald-Stadler
2016-01-25 20:24     ` Andrew F. Davis
2016-01-25 17:28 ` [PATCH v4 2/4] iio: health: Add driver for the TI " Andrew F. Davis
2016-01-25 17:28   ` Andrew F. Davis
2016-01-25 20:17   ` Peter Meerwald-Stadler
2016-01-25 20:30     ` Andrew F. Davis
2016-01-30 14:59   ` Jonathan Cameron
2016-01-30 14:59     ` Jonathan Cameron
2016-02-02 15:50     ` Andrew F. Davis
2016-02-02 15:50       ` Andrew F. Davis
2016-01-25 17:29 ` [PATCH v4 3/4] Documentation: afe4403: Add DT bindings for the AFE4403 " Andrew F. Davis
2016-01-25 17:29   ` Andrew F. Davis
2016-01-25 17:29 ` [PATCH v4 4/4] iio: health: Add driver for the TI " Andrew F. Davis
2016-01-25 17:29   ` Andrew F. Davis
2016-01-25 20:21   ` Peter Meerwald-Stadler
2016-01-25 20:21     ` Peter Meerwald-Stadler
2016-01-25 20:36     ` Andrew F. Davis
2016-01-25 20:36       ` Andrew F. Davis
2016-01-30 15:10   ` Jonathan Cameron
2016-02-02 17:38     ` Andrew F. Davis [this message]
2016-02-02 17:38       ` Andrew F. Davis

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