Re: [RFC PATCH v1 34/57] sata_sil24: Remove PAGE_SIZE compile-time constant assumption

Niklas Cassel
2024-10-17T09:11:53Z

Hello Ryan,

While I realize that this has not always been consistent,
please prefix the subject with "ata: ", so that it becomes
"ata: sata_sil24: ".

On Mon, Oct 14, 2024 at 11:58:41AM +0100, Ryan Roberts wrote:
> To prepare for supporting boot-time page size selection, refactor code
> to remove assumptions about PAGE_SIZE being compile-time constant. Code
> intended to be equivalent when compile-time page size is active.
>
> Convert "struct sil24_ata_block" and "struct sil24_atapi_block" to use a
> flexible array member for their sge[] array. The previous static size of
> SIL24_MAX_SGE depends on PAGE_SIZE so doesn't work for boot-time page
> size.
>
> Wrap global variables that are initialized with PAGE_SIZE derived values
> using DEFINE_GLOBAL_PAGE_SIZE_VAR() so their initialization can be
> deferred for boot-time page size builds.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
>
> ***NOTE***
> Any confused maintainers may want to read the cover note here for context:
> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/
>
> drivers/ata/sata_sil24.c | 46 +++++++++++++++++++---------------------
> 1 file changed, 22 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/ata/sata_sil24.c b/drivers/ata/sata_sil24.c
> index 72c03cbdaff43..85c6382976626 100644
> --- a/drivers/ata/sata_sil24.c
> +++ b/drivers/ata/sata_sil24.c
> @@ -42,26 +42,25 @@ struct sil24_sge {
> __le32 flags;
> };
>
> +/*
> + * sil24 fetches in chunks of 64bytes. The first block
> + * contains the PRB and two SGEs. From the second block, it's
> + * consisted of four SGEs and called SGT. Calculate the
> + * number of SGTs that fit into one page.
> + */
> +#define SIL24_PRB_SZ (sizeof(struct sil24_prb) + 2 * sizeof(struct sil24_sge))
> +#define SIL24_MAX_SGT ((PAGE_SIZE - SIL24_PRB_SZ) / (4 * sizeof(struct sil24_sge)))
> +
> +/*
> + * This will give us one unused SGEs for ATA. This extra SGE
> + * will be used to store CDB for ATAPI devices.
> + */
> +#define SIL24_MAX_SGE (4 * SIL24_MAX_SGT + 1)
>
> enum {
> SIL24_HOST_BAR = 0,
> SIL24_PORT_BAR = 2,
>
> - /* sil24 fetches in chunks of 64bytes. The first block
> - * contains the PRB and two SGEs. From the second block, it's
> - * consisted of four SGEs and called SGT. Calculate the
> - * number of SGTs that fit into one page.
> - */
> - SIL24_PRB_SZ = sizeof(struct sil24_prb)
> - + 2 * sizeof(struct sil24_sge),
> - SIL24_MAX_SGT = (PAGE_SIZE - SIL24_PRB_SZ)
> - / (4 * sizeof(struct sil24_sge)),
> -
> - /* This will give us one unused SGEs for ATA. This extra SGE
> - * will be used to store CDB for ATAPI devices.
> - */
> - SIL24_MAX_SGE = 4 * SIL24_MAX_SGT + 1,
> -
> /*
> * Global controller registers (128 bytes @ BAR0)
> */
> @@ -244,13 +243,13 @@ enum {
>
> struct sil24_ata_block {
> struct sil24_prb prb;
> - struct sil24_sge sge[SIL24_MAX_SGE];
> + struct sil24_sge sge[];
> };
>
> struct sil24_atapi_block {
> struct sil24_prb prb;
> u8 cdb[16];
> - struct sil24_sge sge[SIL24_MAX_SGE];
> + struct sil24_sge sge[];
> };
>
> union sil24_cmd_block {
> @@ -373,7 +372,7 @@ static struct pci_driver sil24_pci_driver = {
> #endif
> };
>
> -static const struct scsi_host_template sil24_sht = {
> +static DEFINE_GLOBAL_PAGE_SIZE_VAR_CONST(struct scsi_host_template, sil24_sht, {
> __ATA_BASE_SHT(DRV_NAME),
> .can_queue = SIL24_MAX_CMDS,
> .sg_tablesize = SIL24_MAX_SGE,
> @@ -382,7 +381,7 @@ static const struct scsi_host_template sil24_sht = {
> .sdev_groups = ata_ncq_sdev_groups,
> .change_queue_depth = ata_scsi_change_queue_depth,
> .device_configure = ata_scsi_device_configure
> -};
> +});
>
> static struct ata_port_operations sil24_ops = {
> .inherits = &sata_pmp_port_ops,
> @@ -1193,7 +1192,7 @@ static int sil24_port_start(struct ata_port *ap)
> struct device *dev = ap->host->dev;
> struct sil24_port_priv *pp;
> union sil24_cmd_block *cb;
> - size_t cb_size = sizeof(*cb) * SIL24_MAX_CMDS;
> + size_t cb_size = PAGE_SIZE * SIL24_MAX_CMDS;
> dma_addr_t cb_dma;
>
> pp = devm_kzalloc(dev, sizeof(*pp), GFP_KERNEL);
> @@ -1258,7 +1257,6 @@ static void sil24_init_controller(struct ata_host *host)
>
> static int sil24_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
> {
> - extern int __MARKER__sil24_cmd_block_is_sized_wrongly;
> struct ata_port_info pi = sil24_port_info[ent->driver_data];
> const struct ata_port_info *ppi[] = { &pi, NULL };
> void __iomem * const *iomap;
> @@ -1266,9 +1264,9 @@ static int sil24_init_one(struct pci_dev *pdev, const struct pci_device_id *ent)
> int rc;
> u32 tmp;
>
> - /* cause link error if sil24_cmd_block is sized wrongly */
> - if (sizeof(union sil24_cmd_block) != PAGE_SIZE)
> - __MARKER__sil24_cmd_block_is_sized_wrongly = 1;
> + /* union sil24_cmd_block must be PAGE_SIZE */
> + BUG_ON(struct_size_t(struct sil24_atapi_block, sge, SIL24_MAX_SGE) != PAGE_SIZE);
> + BUG_ON(struct_size_t(struct sil24_ata_block, sge, SIL24_MAX_SGE) > PAGE_SIZE);
>
> ata_print_version_once(&pdev->dev, DRV_VERSION);
>
> --
> 2.43.0
>

As you might know, there is an effort to annotate all flexible array
members with their run-time size information, see commit:
dd06e72e68bc ("Compiler Attributes: Add __counted_by macro")

I haven't looked at the DEFINE_GLOBAL_PAGE_SIZE_VAR_CONST macro, but since
sge[] now becomes a flexible array member, I think it would be nice if it
would be possible to somehow use the __counted_by macro.

Other than that, this looks good to me.

Kind regards,
Niklas