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    SubjectRe: [PATCH V2] mmc: core: cd_label must be last entry of mmc_gpio struct
    On Mon, Jul 2, 2018 at 2:42 PM, Linus Walleij <linus.walleij@linaro.org> wrote:
    > On Mon, Jul 2, 2018 at 3:32 AM Anson Huang <Anson.Huang@nxp.com> wrote:

    >> - char cd_label[0];
    >> + char cd_label[];
    >
    > Not that I am the smartest in the world when it comes to how the
    > C compilers work this out.
    >
    > But isn't that equivalent to:
    > char *cd_label;
    > ?

    No.

    sizeof(foo) == bar in the original code and with your change it would be
    sizeof(foo) == bar + sizeof(void *)

    On top of that, the actual memory is going in one chunk and requires
    only one allocation.

    But, I like your below stuff, though comments

    > From facb3799f479bfd4dad99c25c9c5d4c77b14c9b0 Mon Sep 17 00:00:00 2001
    > From: Linus Walleij <linus.walleij@linaro.org>
    > Date: Mon, 2 Jul 2018 13:35:01 +0200
    > Subject: [PATCH] mmc: slot-gpio: Allocate GPIO labels dynamically
    >
    > The use of string pointers in the MMC slot GPIO context is
    > pretty dubious, allocating some 2*len extra bytes for each
    > label of the ro and wp pins.
    >
    > Tidy this up using kasprintf() with dynamic allocation of
    > labels for these strings.
    >
    > Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
    > ---
    > drivers/mmc/core/slot-gpio.c | 15 ++++++++++-----
    > 1 file changed, 10 insertions(+), 5 deletions(-)
    >
    > diff --git a/drivers/mmc/core/slot-gpio.c b/drivers/mmc/core/slot-gpio.c
    > index ef05e0039378..c417801b366e 100644
    > --- a/drivers/mmc/core/slot-gpio.c
    > +++ b/drivers/mmc/core/slot-gpio.c
    > @@ -27,7 +27,7 @@ struct mmc_gpio {
    > bool override_cd_active_level;
    > irqreturn_t (*cd_gpio_isr)(int irq, void *dev_id);
    > char *ro_label;
    > - char cd_label[0];
    > + char *cd_label;
    > u32 cd_debounce_delay_ms;
    > };
    >
    > @@ -47,13 +47,18 @@ int mmc_gpio_alloc(struct mmc_host *host)
    > {

    > size_t len = strlen(dev_name(host->parent)) + 4;

    Do you need this still?

    > struct mmc_gpio *ctx = devm_kzalloc(host->parent,
    > - sizeof(*ctx) + 2 * len, GFP_KERNEL);
    > + sizeof(*ctx), GFP_KERNEL);
    >
    > if (ctx) {
    > - ctx->ro_label = ctx->cd_label + len;
    > ctx->cd_debounce_delay_ms = 200;
    > - snprintf(ctx->cd_label, len, "%s cd", dev_name(host->parent));
    > - snprintf(ctx->ro_label, len, "%s ro", dev_name(host->parent));
    > + ctx->cd_label = devm_kasprintf(host->parent, GFP_KERNEL,
    > + "%s cd", dev_name(host->parent));
    > + if (!ctx->cd_label)
    > + return -ENOMEM;
    > + ctx->ro_label = devm_kasprintf(host->parent, GFP_KERNEL,
    > + "%s ro", dev_name(host->parent));
    > + if (!ctx->ro_label)
    > + return -ENOMEM;
    > host->slot.handler_priv = ctx;
    > host->slot.cd_irq = -EINVAL;
    > }

    --
    With Best Regards,
    Andy Shevchenko

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