Re: [PATCH v2] fbdev: bfin-lq035q1-fb: new Blackfin Landscape LCD EZ-Extender driver

[Mike Frysinger]

On Fri, Sep 25, 2009 at 16:24, Mike Frysinger wrote:
> On Thu, Sep 24, 2009 at 19:32, Andrew Morton wrote:
>> On Thu, 17 Sep 2009 17:37:06 -0400 Mike Frysinger wrote:
>>> +static int lq035q1_control(unsigned char reg, unsigned short value)
>>> +{
>>> + Â Â int ret;
>>> + Â Â u8 regs[3] = {LQ035_INDEX, 0, 0};
>>> + Â Â u8 dat[3] = {LQ035_DATA, 0, 0};
>>> +
>>> + Â Â if (spi_control.spidev) {
>>> + Â Â Â Â Â Â regs[2] = reg;
>>> + Â Â Â Â Â Â dat[1] = value >> 8;
>>> + Â Â Â Â Â Â dat[2] = value & 0xFF;
>>> +
>>> + Â Â Â Â Â Â ret = spi_write(spi_control.spidev, regs, ARRAY_SIZE(regs));
>>> + Â Â Â Â Â Â ret |= spi_write(spi_control.spidev, dat, ARRAY_SIZE(dat));
>>> + Â Â } else
>>> + Â Â Â Â Â Â return -ENODEV;
>>> +
>>> + Â Â return ret;
>>> +}
>>
>> I am suspecting that this function (and the similar ones below) rely
>> upon state within the hardware and will hence misbehave if two
>> instances are run concurrently.
>>
>> Is that correct> ÂIf so, is there locking to prevent this from occurring?
>
> if by "instances" you mean "users" as in "multiple programs
> reading/writing the framebuffer concurrently", then probably. Ârather
> than handle the locking ourselves, it can be pushed to the SPI bus by
> having the regs/dat be transfers in a single message.

hmm there shouldnt be any locking problems here actually.  the spi
access is only to initialize/shutdown, and there is a dedicated CS for
each device.  so i dont think anything here really needs changing
(other than to allocate the spi_control global variable dynamically in
the probe).
-mike
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/