linux-kernel - Re: (EXT) Re: (EXT) Re: [PATCH mmc-next v2] mmc: allow setting slot index via device tree alias

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Message-ID: <936a2a0d85b9bd8455cc1844e264a0d9fc86c5ac.camel@ew.tq-group.com>
Date:   Tue, 25 Aug 2020 14:32:38 +0200
From:   Matthias Schiffer <matthias.schiffer@...tq-group.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Sascha Hauer <s.hauer@...gutronix.de>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: (EXT) Re: (EXT) Re: [PATCH mmc-next v2] mmc: allow setting slot
 index via device tree alias

On Tue, 2020-08-25 at 14:27 +0200, Ulf Hansson wrote:
> On Tue, 25 Aug 2020 at 14:00, Matthias Schiffer
> <matthias.schiffer@...tq-group.com> wrote:
> > 
> > On Tue, 2020-08-25 at 11:39 +0200, Matthias Schiffer wrote:
> > > On Tue, 2020-08-25 at 11:14 +0200, Ulf Hansson wrote:
> > > > On Thu, 20 Aug 2020 at 09:59, Matthias Schiffer
> > > > <matthias.schiffer@...tq-group.com> wrote:
> > > > > --- a/drivers/mmc/core/host.c
> > > > > +++ b/drivers/mmc/core/host.c
> > > > > @@ -387,6 +387,7 @@ struct mmc_host *mmc_alloc_host(int
> > > > > extra,
> > > > > struct device *dev)
> > > > >  {
> > > > >         int err;
> > > > >         struct mmc_host *host;
> > > > > +       int alias_id, min_idx, max_idx;
> > > > > 
> > > > >         host = kzalloc(sizeof(struct mmc_host) + extra,
> > > > > GFP_KERNEL);
> > > > >         if (!host)
> > > > > @@ -395,7 +396,18 @@ struct mmc_host *mmc_alloc_host(int
> > > > > extra,
> > > > > struct device *dev)
> > > > >         /* scanning will be enabled when we're ready */
> > > > >         host->rescan_disable = 1;
> > > > > 
> > > > > -       err = ida_simple_get(&mmc_host_ida, 0, 0,
> > > > > GFP_KERNEL);
> > > > > +       host->parent = dev;
> > > > > +
> > > > > +       alias_id = mmc_get_reserved_index(host);
> > > > > +       if (alias_id >= 0) {
> > > > > +               min_idx = alias_id;
> > > > > +               max_idx = alias_id + 1;
> > > > > +       } else {
> > > > > +               min_idx = mmc_first_nonreserved_index();
> > > > > +               max_idx = 0;
> > > > > +       }
> > > > > +
> > > > > +       err = ida_simple_get(&mmc_host_ida, min_idx, max_idx,
> > > > > GFP_KERNEL);
> > 
> > 
> > One more question I came across when reworking my patch: Do we need
> > a
> > fallback here for the case where the reserved index is already
> > taken?
> > To handle an SD card being replaced while still mounted?
> 
> Removal/insertion of an SD card should be fine, as that doesn't mean
> that the host is removed. In other words, host->index remains the
> same.
> 
> Although, for a bad DT configuration, where for example the same
> aliases id is used twice, a fallback could make sense. On the other
> hand, as such configuration would be wrong, we might as well just
> print a message and return an error.

I don't think this can happen as long as we don't have DTs changing at
runtime: Each alias is a DT property name in /aliases, which can only exist once.


> 
> [...]
> 
> Kind regards
> Uffe