linux-kernel - Re: [PATCH 0/3] mtd: maps: vmu-flash: Fix build and runtime errors

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Message-ID: <b5aa220dee9d7dcecea398ec0e33b4cf@artur-rojek.eu>
Date: Wed, 19 Nov 2025 22:54:34 +0100
From: Artur Rojek <contact@...ur-rojek.eu>
To: Florian Fuchs <fuchsfl@...il.com>
Cc: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>, Miquel Raynal
 <miquel.raynal@...tlin.com>, Richard Weinberger <richard@....at>, Vignesh
 Raghavendra <vigneshr@...com>, linux-mtd@...ts.infradead.org,
 linux-sh@...r.kernel.org, linux-kernel@...r.kernel.org, Rich Felker
 <dalias@...c.org>, Paul Cercueil <paul@...pouillou.net>
Subject: Re: [PATCH 0/3] mtd: maps: vmu-flash: Fix build and runtime errors

On 2025-11-19 22:44, Florian Fuchs wrote:
> On 19 Nov 22:36, Artur Rojek wrote:
>> On 2025-11-18 08:31, John Paul Adrian Glaubitz wrote:
>> > Hi Florian,
>> >
>> > On Mon, 2025-11-17 at 23:44 +0100, Florian Fuchs wrote:
>> > > This small series fixes build and runtime errors in the vmu-flash
>> > > driver
>> > > (enabled by CONFIG_MTD_VMU) and the included maple.h. These changes
>> > > were
>> > > verified on real Dreamcast hardware with a physical VMU. The VMU can
>> > > now
>> > > be successfully probed, read and written with MTD tools like
>> > > mtd_info and
>> > > mtd_debug. Previously, the driver failed to build or crashed during
>> > > probing.
>> > >
>> > > 	bash-5.3# mtdinfo /dev/mtd0
>> > > 	mtd0
>> > > 	Name:                           vmu2.1.0
>> > > 	Type:                           mlc-nand
>> > > 	Eraseblock size:                512 bytes
>> > > 	Amount of eraseblocks:          256 (131072 bytes, 128.0 KiB)
>> > > 	Minimum input/output unit size: 512 bytes
>> > > 	Sub-page size:                  512 bytes
>> > > 	Character device major/minor:   90:0
>> > > 	Bad blocks are allowed:         true
>> > > 	Device is writable:             true
>> >
>> > Thanks again for this series. Before this can be picked up, I would like
>> > again
>> > Artur Rojek to test it on his Dreamcast, so let's loop him in.
>> >
>> > If he confirms the functionality, I'll pick it up. I'll try to get it
>> > reviewed
>> > later this week.
>> >
>> > Adrian
>> 
>> Hi Florian,
>> thanks for this series!
>> 
>> Without the maple port fix, this works as intended only when all
>> four maple ports are populated. I am able to read from multiple VMUs 
>> in
>> various slots.
>> 
>> However, with even one port not populated, it causes a panic:
>> > Maple (null): detected Dreamcast Controller: function 0x1: at (0, 0)
>> > Maple (null): no driver found
>> > Maple (null): detected Dreamcast Controller: function 0x1: at (1, 0)
>> > Maple (null): no driver found
>> > Maple (null): detected Visual Memory: function 0xE: at (0, 1)
>> > Maple (null): no driver found
>> > BUG: unable to handle kernel paging request at 00400000
>> > PC: [<8c2aecee>] maple_send.part.0+0x102/0x1c8
>> > Pgd = (ptrval)
>> > [00400000] *pgd=00000000
>> > Oops: 0000 [#1]
>> > Modules linked in:
>> >
>> > CPU: 0 UID: 0 PID: 11 Comm: kworker/0:1 Not tainted
>> > 6.18.0-rc5-next-20251114-00003-gb6bcd2e803f3 #25 PREEMPT
>> > Workqueue: even maple_dma_handler (events)
>> > PC is at maple_send.part.0+0x102/0x1c8
>> > PR is at maple_send.part.0+0x5c/0x1c8
>> > PC  : 8c2aecee SP  : 8c85bef8 SR  : 40008000 TEA : 00400000
>> > R0  : 0000002c R1  : 003fffc4 R2  : 00400004 R3  : 8c4e3d18
>> > R4  : 8c92c024 R5  : 8c4e3d18 R6  : 0000002b R7  : 8c92c030
>> > R8  : 00000000 R9  : 8c4e3d18 R10 : 00000016 R11 : 8c6aacdc
>> > R12 : 00000007 R13 : 8c914c20 R14 : 8c92c030
>> > MACH: 00000001 MACL: 000006cc GBR : 8c000000 PR  : 8c2aec48
>> >
>> > Call trace:
>> >  [<8c030c50>] process_one_work+0x114/0x290
>> >  [<8c00b6a0>] arch_local_irq_restore+0x0/0x24
>> >  [<8c3dac3a>] schedule+0x22/0x108
>> >  [<8c03144a>] worker_thread+0x27e/0x3bc
>> >  [<8c030b3c>] process_one_work+0x0/0x290
>> >  [<8c0379c2>] kthread+0xde/0x1c0
>> >  [<8c0311cc>] worker_thread+0x0/0x3bc
>> >  [<8c0374fc>] to_kthread+0x0/0x1c
>> >  [<8c00b6a0>] arch_local_irq_restore+0x0/0x24
>> >  [<8c00f200>] ret_from_kernel_thread+0xc/0x14
>> >  [<8c00b698>] arch_local_save_flags+0x0/0x8
>> >  [<8c0418b0>] schedule_tail+0x0/0x78
>> >  [<8c0378e4>] kthread+0x0/0x1c0
>> >
>> > Process: kworker/0:1 (pid: 11, stack limit = (ptrval))
>> > Stack: (0x8c85bef8 to 0x8c85c000)
>> > Bee0:                                                       8c030c50
>> > 8c00b6a0
>> > Bf00: 8c80817c 8c808105 8c8462c0 8c808100 8c4e3d38 8c846280 00000000
>> > 48f0d9a1
>> > Bf20: 8c3dac3a 8c85bf40 8c846280 00000000 8c03144a 8c8462c0 8c846280
>> > 8c4ca36c
>> > Bf40: 8c8462a8 8c4da400 8c4ca388 8c030b3c 8c857ebc 8c80797c 8c0379c2
>> > 8c846280
>> > Bf60: 8c0311cc 8c0374fc 8c857ebc 8c00b6a0 8c807960 8c805b40 00000000
>> > 8c85bf98
>> > Bf80: 48f0d9a1 8c00f200 8c839f08 8c4dbbd8 8c493688 8c82c77c 8c00b698
>> > 00000000
>> > Bfa0: 8c0418b0 00000000 00000000 00000000 00000000 8c805b40 8c0378e4
>> > 00000000
>> > Bfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>> > 00000000
>> > Bfe0: 00000000 00000000 00000000 40008000 00000000 00000000 00000000
>> > 00000000
>> > ---[ end trace 0000000000000000 ]---
>> 
>> This means we can't apply this series without the maple fix, and as 
>> such
>> I'll recommend that this waits until hotplug is fixed.
>> 
>> PS. I don't know if it's down to the same issue, but once I remove and
>> re-attach a VMU, it cannot be read from anymore:
>> > Dreamcast_visual_memory 0:01.E: VMU at (0, 1) is busy
>> 
>> PS. Adding Paul in the CC, he might be interested to test in the 
>> future.
> 
> Hi Artur, thanks for testing!
> 
> I am not sure if the errors you see are related to the changes. The
> fixes only make the VMU code compile at all. Without that, the build
> fails and it crashes instantly.
> 
> So I would say, it is an improvement to the status quo.

I wouldn't say that trading a compilation issue for a runtime crash is
an improvement. It only shows that further works needs to be done before
we can accept both the VMU and maple port fixes, and that both of them
are connected.

That said, great work getting it this far. I am here if you need further
debug. If you'd like, check out #linux-sh IRC channel on libera.chat,
then we can brainstorm this further.

Cheers,
Artur

> 
> Regards,
> Florian