Re: [RFC PATCH 9/9] hw/sd: Allow card size not power of 2 again

From: Warner Losh <wlosh@bsdimp.com>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: "Michal Suchánek" <msuchanek@suse.de>,
	"\"Daniel P . Berrangé\"" <berrange@redhat.com>,
	Qemu-block <qemu-block@nongnu.org>,
	"Bin Meng" <bin.meng@windriver.com>,
	"QEMU Developers" <qemu-devel@nongnu.org>,
	"Philippe Mathieu-Daudé" <f4bug@amsat.org>,
	"Alexander Bulekov" <alxndr@bu.edu>,
	"Niek Linnenbank" <nieklinnenbank@gmail.com>,
	"Tom Yan" <tom.ty89@gmail.com>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>,
	"Warner Losh" <imp@bsdimp.com>
Subject: Re: [RFC PATCH 9/9] hw/sd: Allow card size not power of 2 again
Date: Thu, 24 Jun 2021 10:08:42 -0600	[thread overview]
Message-ID: <F7D2C240-184F-4FAA-B4AD-13B492F6CAA0@bsdimp.com> (raw)
In-Reply-To: <CAFEAcA-x-ZWKM0wEHm0-iqLydtyuFCm2ba+j6RGNwLyB0UEtTw@mail.gmail.com>

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> On Jun 24, 2021, at 4:56 AM, Peter Maydell <peter.maydell@linaro.org> wrote:
> 
> On Thu, 24 Jun 2021 at 11:27, Tom Yan <tom.ty89@gmail.com> wrote:
>> I really think we should get (/ have gotten) things clear first. What
>> exactly is the bug we have been talking about here? I mean like, where
>> does it occur and what's the nature of it.
>> 
>> 1. Is it specific to a certain type / model of backend / physical
>> storage device that will be made use of by qemu for the emulated
>> storage? (I presume not since you mention about image, unless you
>> irrationally related/bound the emulated storage type and the physical
>> storage type together.)
>> 
>> 2. Does it have anything to do with a certain flaw in qemu itself?
>> Like the code that does read/write operation is flawed that it cannot
>> be handled by a certain *proper* backend device?
>> 
>> 3. Or is it actually a bug in a certain driver / firmware blob that
>> will be used by an *emulated* device in the guest? In that case, can
>> we emulate another model so that it won't be using the problematic
>> driver / firmware?
> 
> Definitely agreed -- before we start changing QEMU code we need
> to identify clearly (a) what the real hardware does and (b) what
> the situation was we were originally trying to fix.

Real SD and MMC cards do not have power-of-two constraints in the
number of blocks. None of the SD/MMC bridges I’ve ever dealt with
have a power-of-two constraint on the size of the card. The only
constraint on the size related to the card is the block size.

If non-power-of-2 sized cards fail, that’s a cat-1 sev-1 bug that needs
to be fixed, rather than a warning be generated.

Warner

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