Re: [PATCH] ata: pata_macio: Fix max_segment_size with PAGE_SIZE == 64K

[Niklas Cassel <cassel@kernel.org>]

On Thu, Jun 06, 2024 at 09:14:45PM +1000, Michael Ellerman wrote:
> The pata_macio driver advertises a max_segment_size of 0xff00, because
> the hardware doesn't cope with requests >= 64K.
> 
> However the SCSI core requires max_segment_size to be at least
> PAGE_SIZE, which is a problem for pata_macio when the kernel is built
> with 64K pages.
> 
> In older kernels the SCSI core would just increase the segment size to
> be equal to PAGE_SIZE, however since the commit tagged below it causes a
> warning and the device fails to probe:
> 
>   WARNING: CPU: 0 PID: 26 at block/blk-settings.c:202 .blk_validate_limits+0x2f8/0x35c
>   CPU: 0 PID: 26 Comm: kworker/u4:1 Not tainted 6.10.0-rc1 #1
>   Hardware name: PowerMac7,2 PPC970 0x390202 PowerMac
>   ...
>   NIP .blk_validate_limits+0x2f8/0x35c
>   LR  .blk_alloc_queue+0xc0/0x2f8
>   Call Trace:
>     .blk_alloc_queue+0xc0/0x2f8
>     .blk_mq_alloc_queue+0x60/0xf8
>     .scsi_alloc_sdev+0x208/0x3c0
>     .scsi_probe_and_add_lun+0x314/0x52c
>     .__scsi_add_device+0x170/0x1a4
>     .ata_scsi_scan_host+0x2bc/0x3e4
>     .async_port_probe+0x6c/0xa0
>     .async_run_entry_fn+0x60/0x1bc
>     .process_one_work+0x228/0x510
>     .worker_thread+0x360/0x530
>     .kthread+0x134/0x13c
>     .start_kernel_thread+0x10/0x14
>   ...
>   scsi_alloc_sdev: Allocation failure during SCSI scanning, some SCSI devices might not be configured
> 
> Although the hardware can't cope with a 64K segment, the driver
> already deals with that internally by splitting large requests in
> pata_macio_qc_prep(). That is how the driver has managed to function
> until now on 64K kernels.
> 
> So fix the driver to advertise a max_segment_size of 64K, which avoids
> the warning and keeps the SCSI core happy.
> 
> Fixes: afd53a3d8528 ("scsi: core: Initialize scsi midlayer limits before allocating the queue")
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Closes: https://lore.kernel.org/all/ce2bf6af-4382-4fe1-b392-cc6829f5ceb2@roeck-us.net/
> Reported-by: Doru Iorgulescu <doru.iorgulescu1@gmail.com>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218858
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> ---

Applied to libata/for-6.10-fixes:
https://git.kernel.org/pub/scm/linux/kernel/git/libata/linux.git/log/?h=for-6.10-fixes

With John's Reviewed-by from the other thread:
https://lore.kernel.org/linux-ide/171362345502.571343.9746199181827642774.b4-ty@oracle.com/T/#t


Kind regards,
Niklas