On 6/6/24 20:14, 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@xxxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/ce2bf6af-4382-4fe1-b392-cc6829f5ceb2@xxxxxxxxxxxx/
> Reported-by: Doru Iorgulescu <doru.iorgulescu1@xxxxxxxxx>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218858
> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Looks good.
Reviewed-by: Damien Le Moal <dlemoal@xxxxxxxxxx>
> ---
> drivers/ata/pata_macio.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/ata/pata_macio.c b/drivers/ata/pata_macio.c
> index 817838e2f70e..3cb455a32d92 100644
> --- a/drivers/ata/pata_macio.c
> +++ b/drivers/ata/pata_macio.c
> @@ -915,10 +915,13 @@ static const struct scsi_host_template pata_macio_sht = {
> .sg_tablesize = MAX_DCMDS,
> /* We may not need that strict one */
> .dma_boundary = ATA_DMA_BOUNDARY,
> - /* Not sure what the real max is but we know it's less than 64K, let's
> - * use 64K minus 256
> + /*
> + * The SCSI core requires the segment size to cover at least a page, so
> + * for 64K page size kernels this must be at least 64K. However the
> + * hardware can't handle 64K, so pata_macio_qc_prep() will split large
> + * requests.
> */
> - .max_segment_size = MAX_DBDMA_SEG,
> + .max_segment_size = SZ_64K,
> .device_configure = pata_macio_device_configure,
> .sdev_groups = ata_common_sdev_groups,
> .can_queue = ATA_DEF_QUEUE,
--
Damien Le Moal
Western Digital Research
