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Re: [Qemu-devel] [PATCH v5 5/6] fw_cfg: add generic non-DMA read method
From: |
Laszlo Ersek |
Subject: |
Re: [Qemu-devel] [PATCH v5 5/6] fw_cfg: add generic non-DMA read method |
Date: |
Thu, 5 Nov 2015 17:18:44 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 11/05/15 15:32, Gabriel L. Somlo wrote:
> Introduce fw_cfg_data_read(), a generic read method which works
> on all access widths (1 through 8 bytes, inclusive), and can be
> used during both IOPort and MMIO read accesses.
>
> To maintain legibility, only fw_cfg_data_mem_read() (the MMIO
> data read method) is replaced by this patch. The new method
> essentially unwinds the fw_cfg_data_mem_read() + fw_cfg_read()
> combo, but without unnecessarily repeating all the validity
> checks performed by the latter on each byte being read.
>
> This patch also modifies the trace_fw_cfg_read prototype to
> accept a 64-bit value argument, allowing it to work properly
> with the new read method, but also remain backward compatible
> with existing call sites.
>
> Cc: Laszlo Ersek <address@hidden>
> Cc: Gerd Hoffmann <address@hidden>
> Cc: Marc MarĂ <address@hidden>
> Signed-off-by: Gabriel Somlo <address@hidden>
> ---
>
> I think in this case I'll stick with a single assert for the
> whole bounds check. In the long run, "easy to read" might be
> just a bit more helpful than "in the VERY unlikely event of
> actually triggering this, it will also tell us which side of
> the interval we fell out on"...
>
> Thanks again for all the advice and feedback!
> --Gabriel
>
> hw/nvram/fw_cfg.c | 45 +++++++++++++++++++++++++++++++--------------
> trace-events | 2 +-
> 2 files changed, 32 insertions(+), 15 deletions(-)
>
> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
> index 046fa74..8f566f6 100644
> --- a/hw/nvram/fw_cfg.c
> +++ b/hw/nvram/fw_cfg.c
> @@ -274,6 +274,36 @@ static int fw_cfg_select(FWCfgState *s, uint16_t key)
> return ret;
> }
>
> +static uint64_t fw_cfg_data_read(void *opaque, hwaddr addr, unsigned size)
> +{
> + FWCfgState *s = opaque;
> + int arch = !!(s->cur_entry & FW_CFG_ARCH_LOCAL);
> + FWCfgEntry *e = (s->cur_entry == FW_CFG_INVALID) ? NULL :
> + &s->entries[arch][s->cur_entry & FW_CFG_ENTRY_MASK];
> + uint64_t value = 0;
> +
> + assert(size > 0 && size <= sizeof(value));
> + if (s->cur_entry != FW_CFG_INVALID && e->data && s->cur_offset < e->len)
> {
> + /* The least significant 'size' bytes of the return value are
> + * expected to contain a string preserving portion of the item
> + * data, padded with zeros on the right in case we run out early.
> + * In technical terms, we're composing the host-endian representation
> + * of the big endian interpretation of the fw_cfg string.
> + */
> + do {
> + value = (value << 8) | e->data[s->cur_offset++];
> + } while (--size && s->cur_offset < e->len);
> + /* If size is still not zero, we *did* run out early, so continue
> + * left-shifting, to add the appropriate number of padding zeros
> + * on the right.
> + */
> + value <<= 8 * size;
> + }
> +
> + trace_fw_cfg_read(s, value);
> + return value;
> +}
> +
> static uint8_t fw_cfg_read(FWCfgState *s)
> {
> int arch = !!(s->cur_entry & FW_CFG_ARCH_LOCAL);
> @@ -291,19 +321,6 @@ static uint8_t fw_cfg_read(FWCfgState *s)
> return ret;
> }
>
> -static uint64_t fw_cfg_data_mem_read(void *opaque, hwaddr addr,
> - unsigned size)
> -{
> - FWCfgState *s = opaque;
> - uint64_t value = 0;
> - unsigned i;
> -
> - for (i = 0; i < size; ++i) {
> - value = (value << 8) | fw_cfg_read(s);
> - }
> - return value;
> -}
> -
> static void fw_cfg_data_mem_write(void *opaque, hwaddr addr,
> uint64_t value, unsigned size)
> {
> @@ -485,7 +502,7 @@ static const MemoryRegionOps fw_cfg_ctl_mem_ops = {
> };
>
> static const MemoryRegionOps fw_cfg_data_mem_ops = {
> - .read = fw_cfg_data_mem_read,
> + .read = fw_cfg_data_read,
> .write = fw_cfg_data_mem_write,
> .endianness = DEVICE_BIG_ENDIAN,
> .valid = {
> diff --git a/trace-events b/trace-events
> index 17fbddf..f2f2ce4 100644
> --- a/trace-events
> +++ b/trace-events
> @@ -196,7 +196,7 @@ ecc_diag_mem_readb(uint64_t addr, uint32_t ret) "Read
> diagnostic %"PRId64"= %02x
>
> # hw/nvram/fw_cfg.c
> fw_cfg_select(void *s, uint16_t key, int ret) "%p key %d = %d"
> -fw_cfg_read(void *s, uint8_t ret) "%p = %d"
> +fw_cfg_read(void *s, uint64_t ret) "%p = %"PRIx64
> fw_cfg_add_file(void *s, int index, char *name, size_t len) "%p #%d: %s (%zd
> bytes)"
>
> # hw/block/hd-geometry.c
>
Reviewed-by: Laszlo Ersek <address@hidden>
- [Qemu-devel] [PATCH v5 0/6] fw_cfg: spec update, misc. cleanup, optimize read, Gabriel L. Somlo, 2015/11/05
- [Qemu-devel] [PATCH v5 3/6] fw_cfg: remove offset argument from callback prototype, Gabriel L. Somlo, 2015/11/05
- [Qemu-devel] [PATCH v5 5/6] fw_cfg: add generic non-DMA read method, Gabriel L. Somlo, 2015/11/05
- Re: [Qemu-devel] [PATCH v5 5/6] fw_cfg: add generic non-DMA read method,
Laszlo Ersek <=
- [Qemu-devel] [PATCH v5 6/6] fw_cfg: replace ioport data read with generic method, Gabriel L. Somlo, 2015/11/05
- [Qemu-devel] [PATCH v5 2/6] fw_cfg: amend callback behavior spec to once per select, Gabriel L. Somlo, 2015/11/05
- [Qemu-devel] [PATCH v5 4/6] fw_cfg: avoid calculating invalid current entry pointer, Gabriel L. Somlo, 2015/11/05
- [Qemu-devel] [PATCH v5 1/6] fw_cfg: move internal function call docs to header file, Gabriel L. Somlo, 2015/11/05
- Re: [Qemu-devel] [PATCH v5 0/6] fw_cfg: spec update, misc. cleanup, optimize read, Gabriel L. Somlo, 2015/11/23