linux-kernel - Re: [PATCH 2/3] Input/Touchscreen Driver: add support AD7877 touchscreen driver

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Date:	Mon, 15 Oct 2007 13:33:31 -0400
From:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
To:	"Hennerich, Michael" <Michael.Hennerich@...log.com>
Cc:	"Bryan Wu" <bryan.wu@...log.com>,
	linux-input@...ey.karlin.mff.cuni.cz,
	linux-joystick@...ey.karlin.mff.cuni.cz,
	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 2/3] Input/Touchscreen Driver: add support AD7877 touchscreen driver

Hi Michael,

On 10/15/07, Hennerich, Michael <Michael.Hennerich@...log.com> wrote:
> >
> >> +
> >> +static int ad7877_read(struct device *dev, u16 reg)
> >> +{
> >> +       struct spi_device       *spi = to_spi_device(dev);
> >> +       struct ser_req          *req = kzalloc(sizeof *req,
> GFP_KERNEL);
> >
> >How many reads can happen at once? Maybe allocate 1 ser_req per
> >touchcsreen when creating it?
>
> ad7877_read_adc, ad7877_read and ad7877_write are just used by the sysfs
> hooks. Touchscreen samples are read by the kthread using a different
> message struct. So far each sysfs invocation got its own storage for the
> spi message, which then is handed over to the SPI bus driver.
> The SPI bus driver serializes transfers in a kthread.
>
> Two different processes could access the drivers sysfs hooks.
>
> Using one ser_req per touch screen could require additional locking?
> Things at is, looks pretty safe to me.
>

OK, fair enough.

-- 
Dmitry
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