Re: [PATCH v6 1/3] spi/pl022: Add chip select handling via GPIO

[Linus Walleij <linus.walleij@linaro.org>]

On Sat, Sep 1, 2012 at 1:14 PM, shiraz hashim
<shiraz.linux.kernel@gmail.com> wrote:
> Hi Roland,
>
> On Wed, Aug 22, 2012 at 7:19 PM, Roland Stigge <stigge@antcom.de> wrote:
>> @@ -2016,6 +2030,8 @@ pl022_probe(struct amba_device *adev, co
>>         pl022->master_info = platform_info;
>>         pl022->adev = adev;
>>         pl022->vendor = id->data;
>> +       /* Point chipselects to allocated memory beyond the main struct */
>> +       pl022->chipselects = (int *) pl022 + sizeof(struct pl022);
>
> This is going beyond memory allocated for chipselects
> as it adds 4 * sizeof(struct pl022) bytes to pl022.

Yes that is why the allocation looks like this:

+       master = spi_alloc_master(dev, sizeof(struct pl022) + sizeof(int) *
+                                 platform_info->num_chipselect);

> pl022->chipselects = (int *) &pl022[1];
> can be musch safer.

I see absolutely no sematic difference between these two
methods to reach the first position beyond the first struct.

If we're gonna be debating this it's a safe sign that this is
not a good design pattern at all, so then it is better to simply
devm_kzalloc(sizeof(int) * platform_info->num_chipselect);
separately.

(But I'm happy with the patch as it is. And the other way
too, since I'm not very picky.)

Yours,
Linus Walleij